TECHNICAL FIELD OF THE INVENTION

The invention relates to the field of wearable devices and, in particular, relates to a method and apparatus for verifying whether to change a determined wearing status of a wearable device.

BACKGROUND TO THE INVENTION

The health and wellbeing of a subject often needs to be monitored. This is particularly the case in elderly subjects. Monitoring the health and wellbeing of a subject is useful in that it can provide an indication of whether the subject requires assistance.

However, at the same time, it is important that a subject can stay living independently.

A device designed to be worn by the subject can allow a subject to maintain their independence, whilst offering peace of mind to both the subject and a caregiver. For example, the wearable device may be configured to provide immediate access to emergency assistance. An example system in which a wearable device is used in this way is a personal emergency response system (PERS). In a PERS system, the wearable device is often in the form of a pendant that is worn around the neck of the subject and includes an emergency help button (PHB) can be pushed by the subject at any time. This can be particularly helpful where the subject becomes unwell or falls. Falls are a major health problem, especially among the elderly, and can result in severe injury or even death. For this reason, some personal emergency response system have been provided with automatic fall detection technology. The automatic fall detection technology can include inertial sensors (for example, accelerometers) and pressure sensors in the wearable device, which may be included in addition to an emergency help button.

In order to use an emergency help button on a wearable device in case of an emergency (such as a fall), it is important that a subject wears the device. It is thus useful to monitor wearing compliance (i.e. whether the subject is wearing the device). Where the device comprises automatic fall detection sensors, the sensors can be used up to a certain degree to monitor the wearing compliance. The time periods in which it is determined that the subject is not wearing the device (i.e. when the device is a non-wearing status) can be recorded and analysed. For example, a wearing compliance report can be created with these time periods to be used by caregivers to provide support to the subject. The wearing compliance report may indicate that the device is not often worn, or not worn at particular times, which can signal the caregiver to talk to the subject to raise the wearing compliance and thus improve the safety of the subject.

Although some current wearable devices are provided with sensors and the sensors may provide useful information, the sensors also have certain limitations. For example, the sensors can be used to measure the activity of the subject and determine that the device is worn (i.e. is in a wearing status) where some form of activity is measured.

However, the distinction between a wearing status and a non- wearing status is difficult, if not impossible, where the subject is static such as sitting or lying.

US 2014/0288436 Al discloses a biometric monitoring device configured to determine whether the biometric monitoring device is actually being worn by a person. A determination that the biometric monitoring device is not being worn is made when motion data collected from motion sensors of the biometric monitoring device indicate that the biometric monitoring device is substantially immobile (for example, not even demonstrating small movements experienced when the wearer is sleeping or sedentary), or when data from a heartbeat waveform sensor indicates that no heart rate is detected.

However, this does not always provide a reliable determination of whether a subject is wearing the device. For example, a lack of motion detection may be due to events other than the device not being worn. These events may include events where a subject has been taken ill or has fallen. Similarly, a lack of heart rate may also be due to events other than the device not being worn. These events may include events where the subject's heart has stopped (for example, due to a cardiac event such as a heart attack) or where the device is caused to be away from the skin (for example, due to a fall). Even a determination that a subject is wearing the device may be an inaccurate determination since motion and/or an apparent heart rate may be the result of interference or noise. For example, the device may be placed in a location where motion and an apparent heart rate is detected from the surroundings. For example, the device may be placed in a pocket, a bag, on a table or in a moving object such as a car. This can give a false result that the subject is wearing the device.

Therefore, there is a need for a method and apparatus that can provide a more reliable determination of whether a device is worn by a subject. SUMMARY OF THE INVENTION

As noted above, a limitation with existing approaches is that false determinations of whether a subject is wearing a device are made. The invention provides a more reliable determination of whether a device is worn by a user, avoiding and even eliminating false determinations.

Therefore, according to a first aspect of the invention, there is provided a method for verifying whether to change a determined wearing status of a device. The method comprises acquiring a first sensor signal and acquiring a second sensor signal, wherein the first sensor signal and the second sensor signal are indicative of whether a subject is wearing a device. The method also comprises determining a wearing status of the device based on the acquired first sensor signal, the wearing status of the device indicating whether the subject is wearing the device or not wearing the device, and verifying whether to change the determined wearing status of the device based on the acquired second sensor signal. When the wearing status indicates that the subject is not wearing the device and it is verified to change the determined wearing status, the method further comprises outputting a signal indicative that the subject requires assistance.

There is provided a method for verifying whether to change a determined wearing status of a device, the method comprising: acquiring a first sensor signal and acquiring a second sensor signal, wherein the first sensor signal and the second sensor signal are indicative of whether a subject is wearing a device; determining a wearing status of the device based on the acquired first sensor signal, the wearing status of the device indicating whether the subject is wearing the device or not wearing the device; and verifying whether to change the determined wearing status of the device based on the acquired second sensor signal.

In some embodiments, when the wearing status indicates that the subject is wearing the device and it is verified to change the determined wearing status, or when the wearing status indicates that the subject is not wearing the device and it is verified not to change the determined wearing status, the method may further comprise outputting a signal indicative that the subject is not wearing the device.

In some embodiments, when the wearing status indicates that the subject is not wearing the device and it is verified to change the determined wearing status, the method may further comprise outputting a signal indicative that the subject requires assistance. In some embodiments, the method may further comprise detecting a property of the acquired first sensor signal that is uncharacteristic of the determined wearing status for the device.

In some embodiments, the method may further comprise, upon detecting a property of the acquired first sensor signal that is uncharacteristic of the determined wearing status for the device, comparing the acquired first sensor signal to an expected sensor signal that is characteristic of the determined wearing status of the device.

In some embodiments, comparing the acquired first sensor signal to an expected sensor signal may comprise determining whether the acquired first sensor signal has a predefined characteristic in common with the expected sensor signal.

In some embodiments, when it is determined that the first sensor signal has the predefined characteristic in common with the expected sensor signal, the method may comprise validating the determined wearing status of the device, and verifying whether to change the determined wearing status of the device may comprise verifying whether to change the validated wearing status of the device based on the acquired second sensor signal.

In some embodiments, when it is determined that the first sensor signal lacks the predefined characteristic in common with the expected sensor signal, the method may comprise determining that the acquired first sensor signal comprises a noise signal.

In some embodiments, the method may further comprise removing the noise signal from the acquired first sensor signal and determining a validated wearing status of the device based on the acquired first sensor signal with the noise signal removed, wherein verifying whether to change the determined wearing status of the device may comprise verifying whether to change the validated wearing status of the device based on the acquired second sensor signal.

In some embodiments, the method may further comprise acquiring a third sensor signal indicative of whether the subject is wearing the device, wherein verifying whether to change the determined wearing status of the device may comprise verifying whether to change the determined wearing status of the device based on the acquired second sensor signal and the acquired third sensor signal.

In some embodiments, the acquired sensor signals may comprise one more of a physiological characteristic sensor signal, a motion sensor signal, and a pressure sensor signal.

According to a second aspect of the invention, there is provided a computer program product comprising a computer readable medium, the computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method described above.

According to a third aspect of the invention, there is provided an apparatus for verifying whether to change a determined wearing status of a device. The apparatus comprises a control unit configured to: acquire a first sensor signal and acquire a second sensor signal, wherein the first sensor signal and the second sensor signal are indicative of whether a subject is wearing a device. The control unit is also configured to determine a wearing status of the device based on the acquired first sensor signal, the wearing status for the device indicating whether the subject is wearing the device or not wearing the device, and verify whether to change the determined wearing status of the device based on the acquired second sensor signal. When the wearing status indicates that the subject is not wearing the device and it is verified to change the determined wearing status, the control unit is further configured to output a signal indicative that the subject requires assistance.

There is provided an apparatus verifying whether to change a determined wearing status of a device, the apparatus comprising a control unit configured to: acquire a first sensor signal and acquire a second sensor signal, wherein the first sensor signal and the second sensor signal are indicative of whether a subject is wearing a device; determine a wearing status of the device based on the acquired first sensor signal, the wearing status for the device indicating whether the subject is wearing the device or not wearing the device; and verify whether to change the determined wearing status of the device based on the acquired second sensor signal.

In some embodiments, the control unit may be configured to acquire the first sensor signal and the second sensor signal by controlling one or more sensors to acquire the first sensor signal and the second sensor signal.

In some embodiments, the device may comprise the one or more sensors.

There is thus provided an improved method and apparatus that enables a more reliable determination of whether a device is worn by a user. The sensor signals are not only acquired to determine whether the subject is wearing the device, one or more sensor signals are used to validate another sensor signal. By validating sensor signals, the wearing status that is determined is more reliable. This avoids and even eliminates false determinations of wearing status.

In this way, it is possible to increase the accuracy of providing notifications to a subject to encourage wearing compliance. It is also possible to increase the accuracy of providing notifications to another person (such as a care giver, a healthcare provider, a family member, an emergency contact person, or any other person) to indicate that the subject requires assistance.

Moreover, information on the health of the subject can be obtained through the signals acquired, which can aid a person in providing the appropriate care or response to the subject.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

Figure 1 is a block diagram of an apparatus according to an embodiment; Figure 2 is a device worn by subject according to an embodiment; Figure 3 is a flow chart illustrating a method according to an embodiment; Figure 4 is a flow chart illustrating a method according to an embodiment;

Figure 5 is an illustration of a predefined characteristic according to an embodiment;

Figure 6 is an illustration of another predefined characteristic according to an embodiment;

Figure 7 is a graph illustrating a photoplethysmography (PPG) signal according to an embodiment;

Figure 8 is a graph illustrating a noise signal according to an embodiment; Figure 9 is a graph illustrating another noise signal according to an embodiment;

Figure 10 is a graph illustrating sensor signals according to an embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As noted above, the invention provides an improved method and apparatus for determining whether a subject is wearing a device, which enables a more a reliable determination of the correct wearing status of the device. The device can be any device that is designed to be worn by a subject (such as a user, a patient, or any other subject). In other words, the device is a wearable device.

In some embodiments, the device can be designed to be worn on or around the neck of the subject, the wrist of the subject, the waist of the subject, the back of the subject, the chest of the subject, or any other part of the subject. In the neck- worn embodiment, the device can be in the form of a pendant that is worn on a cord, chain, necklace, or collar around the neck of the subject. In the wrist- worn embodiment, the device may be provided in the form of a wrist band, a wrist strap or a watch. Although examples of the form that the device may take have been provided, it will be appreciated that the device is not limited to these forms and other forms of device are also possible.

The device may be a certain type of device. In some embodiments, the device may be an activity monitoring device. The activity monitoring device can be configured to monitor a subject during exercise programs, during walking (e.g. pedometers), during general daily activities, or to detect the occurrence of specific events such as the user falling and/or the user getting out of bed. In some embodiments, the device may be a support device. The support device can be configured to communicate with another device to signal that a subject requires assistance or to raise an alarm. In some embodiments, the support device can include a button operable by the subject. For example, pressing the button of the support device may cause the device to send a signal indicating that the subject requires assistance to another device such as a device of a care giver, a healthcare provider, a family member, an emergency contact person, or any other person. In some embodiments, the device may be provided with both the activity monitoring and support features described.

Although examples of the type of device have been provided, it will be appreciated that the device is not limited to these types of device and the any other type of device suitable to be worn by the user is also possible or any device for which it is desirable or useful to determine whether a subject is wearing the device.

An example device is described in more detail later with reference to Figure 2. Figure 1 shows a block diagram of an apparatus 100 according to an embodiment that can be used for verifying whether to change a determined wearing status of a device (specifically, a wearable device).

The apparatus 100 comprises a control unit 102 that controls the operation of the apparatus 100 and that can implement the method described herein. The control unit 102 can comprise one or more processors, processing units, multi-core processors or modules that are configured or programmed to control the apparatus 100 in the manner described herein. In particular implementations, the control unit 102 can comprise a plurality of software and/or hardware modules that are each configured to perform, or are for performing, individual or multiple steps of the method according to embodiments. In some embodiments, the apparatus 100 is external to (i.e. separate to or remote from the wearable device). In these embodiments, the apparatus 100 may comprise a communications interface component 106 for enabling the apparatus 100 to communicate with any sensors and devices that are external to the apparatus 100 (such as sensors included in or on the wearable device). The communications interface component 106 may communicate with any sensors and devices wirelessly or via a wired connection. In other embodiments, the apparatus 100 is the wearable device. In other words, the wearable device itself may comprise the control unit 102.

The control unit 102 is configured to acquire a first sensor signal. The control unit 102 is also configured to acquire a second sensor signal. The first sensor signal and the second sensor signal are indicative of whether the subject is wearing the device or not wearing the device. In some embodiments, the control unit 102 is configured to acquire the first sensor signal and the second sensor signal by controlling one or more sensors to acquire the first sensor signal and the second sensor signal. The wearable device may comprise the one or more sensors from which the first sensor signal and the second sensor signal are acquired.

Where the apparatus 100 is external to (i.e. separate to or remote from) the wearable device, the control unit 102 of the apparatus 100 controls the one or more sensors of the wearable device to acquire the first sensor signal and the second sensor signal via a wired or wireless connection. Where the apparatus 100 is the wearable device (i.e. where the wearable device comprises the control unit 102), the control unit 102 controls the one or more sensors via an internal connection.

In some embodiments, the first sensor signal and the second sensor signal may be acquired from the same sensor. In other embodiments, the first sensor signal and the second sensor signal may be acquired from different sensors. For example, the control unit 102 may be configured to acquire the first sensor signal by controlling a first sensor to acquire the first sensor signal and may be configured to acquire the second sensor signal by controlling a second sensor to acquire the second sensor signal.

Figure 2 shows an exemplary device and sensor arrangement according to an embodiment. With reference to Figure 2, the device 202 is worn by subject 200. The device 202 is designed to be worn on or around the neck of the subject 200. Specifically, the device 202 is in the form of a pendant that is worn on a cord (i.e. a band, strap, necklace, or the like) around the neck of the subject 200. The cord comprises a first sensor 204 and a second sensor 206 configured to acquire sensor signals indicative of whether the subject 200 is wearing the device 202. In the illustrated example, the first sensor 204 and the second sensor 206 are positioned on the cord such that when the device 202 is worn, the first sensor 204 and the second sensor 206 are located at either side of the neck of the subject 200. In other examples (not illustrated), one or more sensors may be positioned on the cord such that when the device 202 is worn, the one or more sensors are located at the back of the neck of the subject. In some examples, the sensors are positioned to be distant (i.e. remote or away) from the vertebrae of the subject or next to the vertebrae of the subject. In this way, an improved signal or a stronger signal will be acquired by the sensors than if the sensors are positioned on the vertebrae of the subject.

The sensors are positioned to make contact with the skin of the subject. In some embodiments, at least a part of the cord may be formed of (or may include) a material that increases the resistance or friction between the cord and the skin or clothing of the subject. For example, at least the inside of the cord may be made of or include materials such broadcloth, rubber, or similar. In some embodiments, at least a part of the cord may include a tacky, adhesive or sticky surface. These embodiments can help to prevent the cord and the pendant, and thus any integrated sensors, from losing contact with the skin due to movements of the subject (for example, when the subject is falling, walking, running, or any other movements of the subject that may cause the sensors to lose contact with the skin).

In some embodiments, the pendant may comprise a sensor. The positions of the sensors on the cord may be adjustable or may be fixed. Although some example device and sensor arrangements have been provided, it will be understood that other arrangements are also possible.

In some embodiments, the control unit 102 can also be configured to acquire a third sensor signal indicative of whether the subject is wearing the wearable device. In some embodiments, the third sensor signal may be acquired from the same sensor as the first sensor signal and/or the same sensor as the second sensor signal. In other embodiments, the third sensor signal be acquired from a different sensor to the first sensor signal and the second sensor signal. For example, the control unit 102 of the apparatus 100 may be configured to acquire the third sensor signal by controlling a third sensor to acquire the third sensor signal.

The wearable device may comprise the third sensor. Where the apparatus 100 is external to (i.e. separate to or remote from) the wearable device, the control unit 102 of the apparatus 100 may control the third sensor to acquire the third sensor signal via a wired or wireless connection. Where the apparatus 100 is the wearable device (i.e. where the wearable device comprises the control unit 102), the control unit 102 controls the third sensor via an internal connection.

Although examples of acquiring two or three sensor signals indicative of whether the subject is wearing the device have been provided, it will be understood that any other number of sensor signals indicative of whether the subject is wearing the device can be acquired. Also, although examples of one, two or three sensors for acquiring the sensor signals indicative of whether the subject is wearing the device have been provided, it will be understood that any other number of sensors are possible.

A sensor (which may be the first sensor, the second sensor or the third sensor mentioned above) may be any sensor suitable to acquire signals indicative of whether a subject is wearing a device. For example, a sensor may be a vital signs or physiological characteristic sensor (such as a heart rate sensor, a skin conductivity sensor, a muscle activity sensor, a skin temperature sensor, or any other physiological characteristic sensor), an activity or motion sensor (such as an accelerometer, a gyroscope, a magnetometer, or any other motion sensor), a height detection sensor (such as an air pressure sensor, a barometer, or any other height detection sensor), or any other type of sensor suitable to acquire signals indicative of whether a subject is wearing a device.

In some embodiments, a physiological characteristic sensor in the form of a heart rate sensor may be used, where the control unit 102 controls the heart rate sensor to acquire signals indicative of whether a subject is wearing a device. In this embodiment, the signals indicative of whether a subject is wearing a device are heart rate signals. The heart rate sensor may be any type of heart rate sensor.

In one example, the heart rate sensor may be an electrocardiogram (ECG) sensor and the heart rate signal of the subject may be acquired from an ECG signal (i.e. a signal representing the electrical activity of the heart) measured by the ECG sensor. An ECG signal is received from the subject when the device is being worn. The ECG sensor may comprise one or more electrodes. In one exemplary embodiment, the ECG sensor may comprise two electrodes and the electrodes may be located on either side of the neck of the subject. For example, as shown in Figure 2, a first electrode 206 and a second electrode 204 may be integrated at different locations on a cord designed to be worn around the neck of the subject. Alternatively, a first electrode may be positioned on or in the cord and a second electrode may be positioned on or in the pendant. Although examples have been provided for the electrode arrangement, those skilled in the art will be aware of other arrangements for the electrodes to acquire a heart rate signal indicative of whether a subject is wearing a device. In another example, the heart rate sensor may be a photoplethysmography (PPG) sensor and the heart rate signal of the subject may be acquired from a PPG signal measured by the PPG sensor. The PPG sensor may comprise one or more light sources (such as LEDs) operating at specific frequencies and one or more light detectors (such as photo- diodes), which react to the light that is either reflected or transmitted when the PPG sensor is in contact with the skin of the subject. The PPG signal may be obtained from a wrist, finger, hand, forearm or ear of the subject. A PPG signal is measured from the subject when the device is being worn.

In other examples, the heart rate sensor can be an accelerometer integrated into a cord designed to be worn around the neck of the subject or into a pendant on the cord such that the accelerometer is located on the chest of the subject. In these examples, an acceleration measurement signal can be processed to identify accelerations or movements due to the beating of the heart. In other examples, the heart rate sensor can be a microphone integrated into the cord or into a pendant on the cord such that the microphone is located on the chest of the subject. In these examples, a sound measurement signal can be processed to identify sounds that occur due to the beating of the heart.

In some embodiments, a physiological characteristic sensor in the form of a skin conductivity sensor may be used, where the control unit 102 controls the skin conductivity sensor to acquire signals indicative of whether a subject is wearing a device. In this embodiment, the signals indicative of whether a subject is wearing a device are skin conductivity signals (i.e. galvanic skin response signals). Skin conductance can be measured using a pair of electrodes that are placed in contact with the skin of the subject. An electrical current may be applied through one of the electrodes and the resistance of the skin measured, or the voltage between the electrodes can be measured.

As mentioned earlier, other examples of physiological characteristic sensor can include a muscle activity sensor for acquiring muscle activity signals of the subject indicative of whether a subject is wearing a device (such as an electromyograph for acquiring electromyography, EMG, signals) and a skin temperature sensor for acquiring skin temperature signals of the subject indicative of whether a subject is wearing a device.

In some embodiments, a sensor in the form of a motion sensor (such an accelerometer) can be used to acquire signals indicative of whether a subject is wearing a device. The motion sensor may be integrated into a cord designed to be worn around the neck of the subject or into a pendant on the cord such that the motion sensor is located on the chest of the subject. There may be more than one motion sensor, each motion sensor located at a different position on the cord or in the pendant to be located at different parts on the chest of the subject. In these examples, an acceleration measurement signal can be processed to identify accelerations or movements due to respiration or due to the subject moving.

In some embodiments, a sensor in the form of a height detection sensor can be used to acquire signals indicative of whether a subject is wearing a device. For example, the height detection sensor may be an air pressure sensor that measures air pressure or changes in air pressure, which can be processed to determine a height or height change. The height detection sensor may be integrated into a cord designed to be worn around the neck of the subject or into a pendant on the cord such that the height detection sensor moves with the subject. There may be more than one height detection sensor.

Although some examples have been provided above for the sensors and their arrangement, those skilled in the art will be aware of sensors and other types of sensor that can be used to acquire signals indicative of whether a subject is wearing a device and other arrangements for the sensors. In some embodiments, as mentioned earlier, multiple types of sensor can be used to acquire signals indicative of whether a subject is wearing a device.

Referring again to Figure 1, in some embodiments, the apparatus 100 may comprise a memory unit 104 configured to store program code that can be executed by the control unit 102 to perform the method described herein. The memory unit 104 can also be used to store information, data, signals and measurements made or acquired by any sensors or devices that are part of the apparatus 100 or that are external to the apparatus 100.

In some embodiments, the apparatus 100 may comprise a communications interface component 106 for enabling the apparatus 100 to communicate with any sensors and devices (such as the sensors configured to acquire the sensor signals indicative of whether a subject is wearing a device) that are external or internal to the apparatus 100. The communications interface component 106 may communicate with any sensors and devices wirelessly or via a wired connection.

In some embodiments, the apparatus 100 may comprise at least one user interface component 108 for use in providing the subject or other user of the apparatus 100 (for example, a care giver, a healthcare provider, a family member, an emergency contact person, or any other person) with information resulting from the method according to the invention. The user interface component 108 can comprise any component that is suitable for providing the information resulting from the method according to the invention, and can be, for example, any one or more of a display screen or other visual indicator, a speaker, one or more lights, and a component for providing tactile feedback (e.g. a vibration function). The user interface component 108 may be or may comprise means that enables the subject or another user of the apparatus 100 to interact with and/or control the apparatus 100. For example, the user interface component 108 may comprise a switch, a button or other control means for controlling, activating and/or deactivating the apparatus 100 and/or the process of acquiring sensor signals.

It will be appreciated that Figure 1 only shows the components required to illustrate this aspect of the invention, and in a practical implementation the apparatus 100 may comprise additional components to those shown. For example, the apparatus 100 may comprise a battery or other power supply for powering the apparatus 100 or means for connecting the apparatus 100 to a mains power supply.

Figure 3 illustrates a method 300 for verifying whether to change a determined wearing status of a device according to an embodiment. The illustrated method 300 can generally be performed by or under the control of the control unit 102.

With reference to Figure 3, at block 302, a first sensor signal is acquired. At block 304, a second sensor signal is acquired. The first sensor signal and the second sensor signal are indicative of whether a subject is wearing a device. The first sensor signal and the second sensor signal can be acquired at the same time. The first sensor signal and the second sensor signal (and any other sensor signal described herein) may comprise a time series of measurements. In this way, the sensor signals can be directly compared at over time or at predetermined times. As discussed earlier, the first sensor signal and the second sensor signal may be acquired from one or more sensors and may be acquired from the same sensor or a different sensor. The wearable device may comprise the sensor signals.

In some embodiments, the first sensor signal and the second sensor signal may be the same type of sensor signal. For example, the first sensor signal and the second sensor signal may both be a physiological characteristic sensor signal, a motion sensor signal, or a pressure sensor signal. In other embodiments, the first sensor signal and the second sensor signal may be different types of sensor signals. For example, the first sensor signal may be a physiological characteristic sensor signal and the second sensor signal may be a motion sensor signal. Although examples are provided, it will be understood that other types of sensor signals and other combinations of sensor signals are also possible.

At block 306, a wearing status of the device is determined based on the acquired first sensor signal. The wearing status of the device indicates whether the subject is wearing the device (i.e. a "wearing" status) or not wearing the device (i.e. a "non-wearing" status). The control unit 102 is configured to determine the wearing status of the device based on the acquired first sensor signal.

At block 308, it is verified whether to change the determined wearing status of the device based on the acquired second sensor signal. The control unit 102 is configured to verify whether to change the determined wearing status of the device based on the acquired second sensor signal. In this way, a more reliable wearing status is provided.

For example, the wearing status of the device determined at block 306 based on the acquired first sensor signal may indicate that the subject is not wearing the device. However, this wearing status may be acquired based on a motion detector signal acquired from a motion detector when the subject is sleeping or sedentary. As such, the determined wearing status of the device is incorrect. The lack of motion detected is not due to the subject not wearing the device but is instead due to the subject being asleep or sedentary. However, by verifying whether to change the determined wearing status of the device at block 308 based on another signal (the acquired second sensor signal), the determined wearing status of the device can be corrected. For example, the acquired second sensor signal may be acquired from a physiological characteristic sensor that will detect a physiological characteristic signal (such as a heart rate signal) indicating that the subject is in fact wearing the device and the determined wearing status can be verified at block 308 by changing it from a status indicating that the subject is not wearing the device to the correct status indicating that the subject is wearing the device.

In another example, the wearing status of the device determined at block 306 based on the acquired first sensor signal may indicate that the subject is not wearing the device. However, this wearing status may be acquired based on no physiological

characteristic sensor signal (for example, a heart rate signal) being received from a physiological characteristic sensor due to the sensor losing contact with the skin (for example, due to the subject falling) or due to the subject becoming ill (for example, due to a heart attack). As such, the determined wearing status of the device is incorrect. The lack of a physiological characteristic sensor signal is not due to the subject not wearing the device but is instead due to the device losing contact with the skin of the subject or the subject becoming ill. However, by verifying whether to change the determined wearing status of the device at block 308 based on another signal (the acquired second sensor signal), the determined wearing status of the device can be corrected. For example, the acquired second sensor signal may be acquired from a motion detector sensor that will detect a higher amplitude motion signal immediately prior to the physiological characteristic sensor signal being lost, which indicates that the subject is in fact wearing the device but has fallen or experienced a medical event (such as a heart attack). The determined wearing status can be verified at block 308 by changing it from a status indicating that the subject is not wearing the device to the correct status indicating that the subject is wearing the device.

In an embodiment when the wearing status indicates that the subject is not wearing the device (at block 306) and it is verified to change the determined wearing status (at block 308), a signal indicative that the subject requires assistance is output. For example, the signal may be an alarm that automatically connects the subject to a call centre. In some embodiments, the signal may automatically connect the subject to the call centre via the wearable device (for example, the wearable device may be equipped with a cell phone and/or audio technology). In some embodiments, the signal may automatically connect the subject to the call centre via another device (such as a communicator box) placed inside the home that is configured to receive the alarm from the wearable device and connect to the call centre. In this way, it is possible for a trained response agent at the call centre to assess the situation and ensure that appropriate assistance is provided to the subject.

In some embodiments, it may initially be detected that the subject puts on the device and a time window (for example, a time window of five seconds) may be set after which the wearing status of the device is determined based on the acquired first sensor signal and verified based on the acquired second sensor signal. This time window can provide more reliable results. For example, an initial high impact detected in an acquired signal may be the result of the device initially contacting with the skin of the subject and is thus not wrongly registered as the subject falling.

In embodiments where a fall is detected or the subject is determined to be unwell, a physiological characteristic signal can provide more information on the status of the subject in cases where the sensors are remain in contact with the skin. This information can be provide in the signal that is output. For example, the physiological characteristic signal may indicate an increased heart rate and/or an increased respiration rate for the subject. In this example, the output signal can include an indication that the subject is experiencing stress, anxiety and/or pain. In another example, the physiological characteristic signal may indicate no significant increase in heart rate and/or no significant increase in breathing rate for the subject. In this example, the output signal can include an indication that the subject is unresponsive. In another example, the physiological characteristic signal may indicate a reduced heart rate and/or a reduced breathing rate for the subject. In this example, the output signal can include an indication that the subject requires immediate medical attention. In this way, it is possible to provide a reliable indication of the health status of the subject, which may prove to be vital in assisting the subject.

In an embodiment when the wearing status indicates that the subject is wearing the device (at block 306) and it is verified to change the determined wearing status (at block 308), a signal indicative that the subject is not wearing the device is output.

Similarly, in an embodiment when the wearing status indicates that the subject is not wearing the device (at block 306) and it is verified not to change the determined wearing status (at block 308), a signal indicative that the subject is not wearing the device is output. In some embodiments, the signal is at least one of an alarm (for example, to notify the subject to wear the device) and an instruction to store the "not- wearing" status. The "not- wearing" status may be stored with associated information such as the time of the status and the duration for which the subject is not wearing the device. The stored status and any associated information can be communicated to at least one of the subject and a caregiver at set time periods (for example, in the form of weekly reports, monthly reports, or similar). In this way, the subject and/or the caregiver is provided with information that can be used for data analysis and predictive models.

In an embodiment when the wearing status indicates that the subject is wearing the device (at block 306) and it is verified not to change the determined wearing status (at block 308), no signal is output. The process may then be ended or repeated (for example, after a set period of time or continuously).

In this way, by adding additional information (from other sensor signals) into the processing and analysis in the manner described above, it can be ensured that the correct classification of wearing status is made. It can also be ensured that appropriate action can be taken in cases where the subject requires assistance. The signals acquired by way of the invention may also be used to analyse the health status of the subject over time (such as the activity levels, energy expenditure, fitness levels, any functional decline, or similar). This information can be communicated to a user of the apparatus (such as a care giver, a healthcare provider, a family member, an emergency contact person, or any other person) and used to improve the care management provided to the subject.

The method of Figure 3 may be repeated. In one embodiment, the method of

Figure 3 is repeated automatically on expiry of a time period. The time period may be a pre- configured time period or may be a time period set by an operator (such as the subject themselves, a family member or a healthcare professional). In another embodiment, the method of Figure 3 is repeated on instruction by an operator (for example, via a user interface component).

Figure 4 illustrates a method 400 for verifying whether to change a determined wearing status of a device according to another embodiment. The illustrated method 400 can generally be performed by or under the control of the control unit 102 of the apparatus 100.

At blocks 402, 404 and 406 of Figure 4, the process steps described with respect to blocks 302, 304 and 306 of Figure 3 are performed respectively and will thus not be repeated here.

At block 408 of Figure 4, a property of the acquired first sensor signal is detected that is uncharacteristic of the determined wearing status for the device. The property can be any property that is uncharacteristic of the wearing status that is determined for the device (at block 406). Examples of the property may include a level of motion that is below an expected level for the motion, a heart rate that is above an expected value for the heart rate, a skin temperature that is above an expected value for the skin temperature, unexpected variations in the heart rate or skin temperature, or similar. Although examples have been provided for the property, it will be understood that other properties may also be detected that are uncharacteristic of the determined wearing status for the device. In some embodiments, the property may be determined to be uncharacteristic if it is detected for more than a threshold time period.

At block 410, upon detecting a property of the acquired first sensor signal that is uncharacteristic of the determined wearing status for the device, the acquired first sensor signal is compared to an expected sensor signal that is characteristic of the determined wearing status of the device. In other words, the acquired first sensor signal is compared to a template signal. Since block 410 is performed where a property of the acquired first sensor signal is detected that is uncharacteristic of the determined wearing status for the device, it is possible to reduce power consumption by only performing the comparison where there is doubt over the accuracy of the determined wearing status. However, it will be understood that in other embodiments, the comparison may be performed continuously (i.e. not only on detecting an uncharacteristic property).

The comparison of the acquired first sensor signal to the expected sensor signal may comprise determining whether the acquired first sensor signal has a predefined characteristic in common with the expected sensor signal (at block 412). In other words, it is determined whether there are characteristics in the acquired first sensor signal that are recognisable characteristics of the sensor signal that are expected for the determined wearing status. For example, in the embodiment where the first sensor signal is an ECG signal, the predefined characteristic is a recognisable characteristic from a template ECG signal.

Similarly, in the embodiment where the first sensor signal is a PPG signal, the predefined characteristic is a recognisable characteristic from a template PPG signal.

The predefined characteristic can be used to determine if the acquired first sensor signal is a true signal or if the first sensor signal includes noise. If the predefined characteristic of the template sensor signal is found to be present in an acquired sensor signal, the acquired sensor signal is determined to be a true signal. If the predefined characteristic of the template sensor signal is found to be absent from an acquired sensor signal, the acquired sensor signal is determined to be a noise signal. In this way, noise signals will no longer be mistaken for true signals and can be avoided in determining a validated wearing status, which will be explained in more detail below.

Figure 5 is an illustration of a template ECG signal according to an

embodiment. The predefined characteristic according to this embodiment, may be the QRS pattern of the template ECG signal, the PQRST pattern of the template ECG signal, or any other pattern distinct to the template ECG signal. If the predefined characteristic of the template ECG signal is found to be present in an acquired ECG signal, the acquired ECG signal is determined to provide a true indication of the wearing status. If the predefined characteristic of the template ECG signal is found to be absent from an acquired ECG signal, the acquired ECG signal is determined to comprise noise.

Figure 6 is an illustration of a template PPG signal according to an embodiment. The predefined characteristic according to this embodiment, may be the recurring ABCD pattern (where A is a maximum amplitude, B is a dicrotic notch, C is a peak following the dicrotic notch and D is a minimum amplitude), the steeper gradient in the slope between D and A than between C and D, or any other pattern distinct to the template PPG signal. If the predefined characteristic of the template PPG signal is found to be present in an acquired PPG signal, the acquired PPG signal is determined to provide a true indication of the wearing status. If the predefined characteristic of the template PPG signal is found to be absent from an acquired PPG signal, the acquired PPG signal is determined to comprise noise.

In the embodiment when it is determined that the first sensor signal has the predefined characteristic in common with the expected sensor signal, the process proceeds to block 414 at which the determined wearing status of the device is validated. The acquired first sensor signal is determined to be a true signal (i.e. rather than a noise signal).

Figure 7 is a graph illustrating an acquired PPG signal according to an embodiment in which the acquired PPG signal is determined to have a predefined

characteristic in common with an expected PPG signal (such as that shown in Figure 6). For example, it can be determined from the acquired PPG signal of Figure 7 that the predefined characteristic of the steeper gradient in slope between D and A than between C and D that is distinct (or common) to an expected PPG signal is present. In this example, the acquired PPG signal is determined to be a true PPG signal and the process proceeds to block 414 at which the determined wearing status of the device is validated.

At block 416, it is verified whether to change the validated wearing status of the device based on the acquired second sensor signal, as discussed above with respect to block 308 of Figure 3. It will be understood that the above description in respect of block 308 of Figure 3 applies also to block 416 of Figure 4 and thus will not be repeated here.

On the other hand, in the embodiment when it is determined that the first sensor signal lacks the predefined characteristic in common with the expected sensor signal (i.e. where it is determined that the predefined characteristic is absent from the first sensor signal), the process proceeds to block 418 at which it is determined that the acquired first sensor signal comprises a noise signal. In other words, it is determined that the acquired first sensor signal is distorted by noise and thus not a true signal.

Figure 8 is a graph illustrating an acquired PPG signal according to an embodiment in which the acquired PPG signal is determined to lack a predefined

characteristic in common with an expected PPG signal (such as that shown in Figure 6). For example, it can be determined from the acquired PPG signal of Figure 8 that the predefined characteristic of the steeper gradient in slope between D and A than between C and D that is distinct (or common) to an expected PPG signal is absent. Instead, the signal has a sinusoidal waveform. In this example, the process proceeds to block 418 at which it is determined that the acquired the acquired PPG signal comprises a noise signal.

Figure 9 is a graph illustrating another acquired PPG signal according to an embodiment in which the acquired PPG signal is determined to lack a predefined

characteristic in common with an expected PPG signal (such as that shown in Figure 6). For example, it can be determined from the acquired PPG signal of Figure 8 that the predefined characteristic of the steeper gradient in slope between D and A than between C and D that is distinct (or common) to an expected PPG signal is absent. In this example, the process proceeds to block 418 at which it is determined that the acquired the acquired PPG signal comprises a noise signal. Such a noise signal may be experienced where the device is placed on a table.

At block 420, the noise signal is removed from the acquired first sensor signal. Any suitable noise removal technique may be used to remove the noise signal. For example, a Chebyshev noise processing technique, a Butterworth filter, an elliptic filter, or any other noise removal technique may be used. Those skilled in the art will be aware of other noise removal techniques that can be used to remove the noise signal from the acquired sensor signal.

At block 422, a validated wearing status of the device is determined based on the acquired first sensor signal with the noise signal removed. In other words, a validated wearing status of the device is determined based on the true first sensor signal.

At block 424, it is verified whether to change the validated wearing status of the device based on the acquired second sensor signal, as discussed above with respect to block 308 of Figure 3 and block 416 of Figure 4. It will be understood that the above description in respect of block 308 of Figure 3 and block 416 of Figure 4 applies also to block 424 of Figure 4 and thus will not be repeated here.

In some embodiments, as discussed earlier, a third sensor signal indicative of whether the subject is wearing the device is acquired. In these embodiments, it is verified (at blocks 308, 416 and 424) whether to change the determined wearing status of the device based on the acquired second sensor signal and the acquired third sensor signal. In other words, the verification is performed using more than one signal.

Figure 10 is a graph illustrating sensor signals according to an embodiment. In this embodiment, a skin temperature signal 1300 is acquired (at block 402 of Figure 4) and a heart rate signal 1304 is acquired (at block 404 of Figure 4). The skin temperature signal 1300 is determined to comprise a noise signal in the form of an ambient temperature signal 1302 (at block 418 of Figure 4). The ambient temperature signal 1302 is removed from the acquired skin temperature signal 1300 to obtain a delta skin temperature signal 1306 (at block 420 of Figure 4). A validated wearing status of the device is determined based on the delta skin temperature signal 1306 (at block 422 of Figure 4). In this embodiment, the delta skin temperature signal 1306 remains above zero and thus a determination is made that the subject is wearing the device.

If, on the other hand, the delta skin temperature signal 1306 reaches zero, it is verified whether to change the validated wearing status of the device based on the acquired heart rate signal 1304 (at block 424). In one example, the delta temperature may reach zero where the subject removes the device (since only ambient temperature is recorded in this case). As the heat rate of the subject is absent in this case, it is determined to change the wearing status of the device to indicate that the subject is not wearing the device. In another example, the delta temperature may reach zero where the ambient temperature approximates the skin temperature. However, where there is a heart rate present, it is determined to maintain the wearing status indicating the subject is wearing the device. This may occur in a situation where the subject is in a warm climate and the skin temperature of the subject reaches the ambient temperature (for example, a temperature of approximately 37 °C) due to the warm climate. This may also occur in a situation where the subject is performing a sport- related activity where the skin temperature is expected to drop initially (during warm-up) and rise afterwards (when the body is warm).

There is thus provided an improved method and apparatus that enables a more reliable determination of whether a device is worn by a user.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless

telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.