TECHNICAL FIELD

The present disclosure relates to a wearable device, and in particular, but not exclusively, to a wearable device for determining a fatigue level of a child and/or for determining when a child is ready to go to sleep. Aspects of the invention relate to a wearable device for determining when a child is ready to go to sleep, to a system for determining when a child is ready to go to sleep and to a method of determining when a child is ready to go to sleep.

BACKGROUND

It is known to use sleep training techniques to help a child, for example a baby or infant to learn to settle themselves to sleep such that they sleep for longer without waking periodically throughout the night. Sleep is important in the development and growth of a child and as such sleep training methods may be adopted to ensure children are getting the required amount and quality of sleep.

Existing sleep training methods are generally split into two main categories, namely controlled crying and a non-cry approach. Both these methods are underpinned by the concept of developing a routine around the child’s bedtime and comforting the child if they fail to get to sleep or wake during the night.

When using the controlled crying approach if the child fails to sleep when initially put down to sleep or if the child wakes during the night the parent will let the child cry for a short, specified period of time before going to comfort and reassure the child. The length of time that the child is allowed to cry for is slowly increased thereby slowly increasing the time available for the child to resettle themselves and to fall asleep. This approach can be undesirable as leaving a child to cry can be distressing for parents and furthermore may risk waking other children within the house who may already be asleep.

The alternative no-cry method is a method used in sleep training that involves parents providing comfort and reassurance to the child by staying in the room once the baby has been put down to sleep until such a time that the child has fallen asleep. Overtime the method involves retreating further away from the child’s bed until the parent is no longer required to stay in the child’s room for them to fall asleep.

Both of these methods involve putting the baby down to sleep and then providing a level of comfort or reassurance to the child in order to help them get to sleep. These methods ultimately rely on the infant being ready to go to sleep or in a state receptive to going to sleep when the parent puts the child down to sleep.

These sleep training methods try to establish a repeatable bed time routine for the child so that, for example, at 19:00 each evening the child will be put down to sleep and the child’s internal body clock will learn that at 19:00 it is time to go to bed. However, a child’s day-to-day experiences vary and thus the time at which the child is ready to go to sleep at will also vary. For example, if the child is stimulated in the afternoon, they may take longer to calm down from the stimulation meaning they are not ready to sleep until 19:30 or later. As such, to maximise the child’s chance of falling asleep in the evening there is a need to determine when the child is ready and receptive to going to sleep.

Existing products seek to predict when an infant will be ready to sleep by tracking events on an app. For example, a parent may log when the infant last ate or last napped and based on the age of the child the app may predict when the child will be ready to sleep that evening. This system can provide a useful indication of when a child will be ready to sleep but the predictions are based on a previous routine and data input to an app which can be unreliable and give an inaccurate prediction of when the infant will be ready to sleep.

Furthermore, the window that a child will ready and receptive to sleep may be about 15 minutes or less. There is therefore a requirement for a system that can accurately predict when a child will be ready to go to sleep and to provide a notification to the parents when the child is ready such that their bedtime routine can be started. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

WO 2018037156 describes a method and system for determining a time window for sleep of a person by measuring a distal skin temperature of the person. The method of WO 2018037156 describes determining an optimal time window for sleep of a person using a temperature change pattern in the form of a drop in the distal skin temperature followed by an increase in the distal skin temperature.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided a wearable device for determining when a child is ready to go to sleep, the device comprising: a temperature sensor configured to measure the temperature of the child; and a control module configured to receive the measured temperature of the child from the temperature sensor; wherein the control module is configured to determine, in dependence on a temperature fluctuation in the received measured temperature, when the child is ready to go to sleep; the temperature fluctuation comprising an increase in the measured temperature of the child followed by a drop in the measured temperature of the child; and the control module is further configured to output a notification signal to generate a notification when the control module determines that the child is ready to go to sleep.

The wearable device is configured to determine when the child is ready to go to sleep or when the child is in a state receptive to sleep. A child may be considered to be ready to go to sleep or in a state receptive to sleep when their melatonin levels have started to increase. An increase in the child’s natural melatonin levels causes the child to become tired and as such it is desirable to start the child’s bedtime routine when their melatonin levels are increasing. As the child’s melatonin levels increase and the child starts to become tired or receptive to going to sleep fluctuations in the child’s temperature may be detected to determine that the child is ready to go to sleep.

The wearable device beneficially predicts when the child is ready to sleep or when the child is in a state receptive to sleep and provides a notification to alert a parent or carer that the child is ready to sleep. The device is configured to determine that the child is ready to go to sleep in response to determining a temperature fluctuation pattern indicative of the child being ready to sleep. The temperature fluctuation pattern may be an increase in the child’s temperature followed by a decrease in the child’s temperature. Determining when the child is ready to go to sleep in dependence on a detected temperature increase followed by a temperature decrease beneficially gives an accurate indication of when the child is ready to sleep due to the rapid decrease in temperature following the increase in temperature. The wearable device may be secured to a child’s limb, for example on their wrist, and the child may be unaware that the device is monitoring their temperature. Furthermore, the notification may be at least one of: a light illuminating on the device, a light changing colour on the device and a notification on a mobile communication device. The notification signal may be output when the control module determines that the child is ready to go to sleep such that the parent or carer can start the child’s bedtime routine.

The temperature fluctuation comprises a drop in the temperature of the child. The drop in temperature of the child is preceded by an increase in the temperature of the child. The temperature fluctuation may be an increase or a decrease of between about 0.1 °C and 1 °C. Determining when the child is ready to sleep in dependence on a temperature fluctuation comprising an increase in temperature followed by a drop in the temperature of the child is beneficial as the fluctuation is relatively large and predictable in a child thereby allowing the device to accurately predict when the child is ready to go to sleep. This is particularly beneficial in children where they can become irrational and prone to tantrums around bedtime and as such when the child is ready to go to sleep the parent or carer should act quickly to ensure that the sleep window is not missed.

Furthermore, the control module may be configured to determine that the child is ready to go to sleep in dependence on the length of time the child has spent asleep previously that day. The control module may be configured to output the notification signal to generate the notification in dependence on the detected temperature fluctuation. For example, the control module may detect a temperature fluctuation indicative of the child being ready to go to sleep and the notification may be generated to alert a parent or carer to start the child’s bedtime routine should be started. The control module may be configured to determine that the child is ready to go to sleep in dependence on the age of the child.

In one embodiment the magnitude of the drop in the measured temperature may be greater than the magnitude of the increase in the measured temperature. The temperature fluctuation comprising an increase in measured temperature followed by a decrease in measured temperature that is greater than the increase beneficially provides an accurate and predictable temperature fluctuation indicative of the child being ready to go to sleep. In an embodiment the wearable device may comprise a light source and the notification signal may be output to the light source to illuminate the light source. Illuminating the light source may comprise transitioning the light source from an OFF state to an ON state. Alternatively, illuminating the light source may comprise changing the colour of the light source.

In one embodiment the control module may be configured to output a second notification signal in response to a second temperature fluctuation being detected by the control module in the measured temperature. The second temperature fluctuation may be a stabilisation of the child’s temperature or it may be an increase in the child’s measured temperature. A second notification signal may be output in response to detecting a second temperature fluctuation. The second notification signal may transition the light source from the ON state to an OFF state or it may change the colour of the light source. For example, the light source may be transitioned from a green light to an orange light. The second notification signal may further or alternatively be output to a mobile communication device to generate a second notification on the mobile communication device.

In an embodiment the second notification signal may be output in response to a stabilisation in the measured temperature of the child. The second notification signal may be indicative of the child being in a state where they are about to transition from being ready to sleep to an overtired state. The control module may be configured to output a third notification signal in response to a further temperature increase following the stabilisation in the measured temperature. The third notification signal may be indicative of the child being in the overtired state. The overtired state may be a point where the child’s fatigue level plateaus and the child has a second wind as a result of a spike in cortisol levels in the child. The spike in cortisol levels has the effect of the tired becoming too tired to sleep or overtired.

The first notification may be output when it is determined that the child’s fatigue level is at a point where the child is ready to go to sleep. The first notification may be output in response to detecting a temperature fluctuation indicative of the child having a fatigue level indicative of the child being ready to sleep. The second notification may be output when the child’s fatigue level continues to rise but before their fatigue level plateaus. The second notification may be output when the child’s temperature has dropped by a pre-determined magnitude or when the child’s temperature has stabilised. The third notification may be output when the child is overtired and no longer receptive to sleep. The third notification signal may be output in response to an increase in the child’s temperature. The first, second and third notifications may be output via a mobile communication device and/or a light source.

In one embodiment the control module may be configured to determine a rate of temperature change in the drop in measured temperature. The control module may be configured to determine the child is ready to go to sleep when the rate of temperature change exceeds a threshold value.

In another embodiment the wearable device may comprise a housing and a strap for securing the wearable device to a limb of the child. The housing may be removably coupled to the strap. The strap may comprise an enclosure for removably securing the housing to the strap. The enclosure may encase a substantial portion of the housing when the housing is received within the enclosure. This is beneficial as encasing the housing with the enclosure may protect the housing from the child. For example, the enclosure may be made from a soft material, such as a soft plastics material like silicone, and the enclosure may serve as a soft material the child can chew. Furthermore, the soft plastics enclosure may protect the housing from damage from bumps or impacts when it is worn on the child’s wrist.

In an embodiment the housing may comprise a port located on a side wall of the housing. A side wall of the enclosure may cover the port when the housing is located within the enclosure. This is beneficial as the side wall of the enclosure may act as a cap or cover to prevent the ingress of objects, dirt or moisture into the port.

In one embodiment the enclosure may comprise an aperture aligned with the light source when the housing is received within the enclosure such that light emitted from the light source may pass through the aperture. This is beneficial as the aperture may convey light from the light source such that the light source is visible when the housing is located within the enclosure. The housing may comprise a window for conveying light from the light source and furthermore the window may protrude at least partially through the aperture when the housing is received within the enclosure. This is beneficial as protruding the window through the aperture may improve the visibility of light emitted from the light source. Alternatively, the window may be substantially flush with the top surface of the housing and the aperture may be aligned with the window. The window may be illuminated by the light source and emit light or glow through the aperture.

In another embodiment the housing may comprise at least one engagement tab and the strap may comprise at least one corresponding engagement formation for securing the housing to the strap. This is beneficial as the tab may engage the engagement formation or slot to retain the housing within the enclosure such that an infant could not remove the housing from the enclosure. The engagement tab may extend from the housing in at least a partially downward direction. As such, the tab may act as a barb preventing removal of the housing from the enclosure without deforming or manipulating the enclosure to disengage the tab from the engagement formation.

In an embodiment a bottom surface of the housing may be exposed such that when the wearable device is secured to the child the bottom surface of the housing contacts the child’s skin. The bottom surface may comprise an opening and the temperature sensor may at least partially be received within the opening such that the temperature sensor contacts the child’s skin when the wearable device is secured to the child. This is beneficial as maintaining contact between the child’s skin and the bottom surface of the housing and/or the temperature sensor improves the accuracy of the measured temperature of the child.

In another embodiment the wearable device may comprise a communication module. The communication module may be configured to transmit the notification signal to a mobile communication device to generate a notification on the mobile communication device. The mobile communication device may be, for example, a mobile phone, a laptop, a tablet, a baby monitor or the like.

According to a further aspect of the present invention there is provided a system for determining when a child is ready to go to sleep, the system comprising: a wearable device as outlined in any one of the aforementioned aspects or embodiments; and a mobile communication device; wherein the control module is configured to output the notification signal to generate the notification on the mobile communication device. According to a yet further aspect of the present invention there is provided a method of determining when a child is ready to go to sleep, the method comprising: measuring a temperature of the child; determining when the child is ready to go to sleep in dependence on a temperature fluctuation in the measured temperature of the child; and outputting a signal to generate a notification when it is determined the child is ready to go to sleep wherein determining when the child is ready to go to sleep comprises detecting a temperature increase in the measured temperature of the child followed by a decrease in the measured temperature of the child.

Determining when the child is ready to go to sleep comprises detecting a decrease in the temperature of the child. Detecting the decrease in the temperature of the child is preceded by detecting an increase in the temperature of the child. The temperature fluctuation is an increase in temperature followed by a decrease in temperature. Determining when the child is ready to go to sleep may comprise determining a rate of increase in the temperature or a rate of decrease in the temperature of the child.

In an embodiment determining the child is in a state receptive to sleep may comprise comparing the temperature fluctuation with a temperature fluctuation pattern. The temperature fluctuation pattern may be selected in dependence on at least one of: an age of the child, a time of day, an expected number of naps, an expected time between naps and a previous measured temperature fluctuation of the child.

In an embodiment the method may comprise determining when the child is about to transition from being ready to sleep to an overtired state. Determining when the child is about to transition to the overtired state comprises detecting a temperature stabilisation in the measured temperature of the child.

In one embodiment the method may further comprise determining when the child is no longer ready to go to sleep in dependence on detecting a further temperature fluctuation. The further temperature fluctuation may comprise a stabilisation in the temperature of the child or an increase in the temperature of the child. Determining when the child is no longer ready to go to sleep may comprise determining that the child has fallen asleep in dependence on the second temperature fluctuation. Alternatively, determining when the child is no longer ready to go to sleep may comprise that the child is overtired and not in a state receptive to sleep in dependence on the second temperature fluctuation. The further temperature fluctuation may follow the stabilisation in the measured temperature and the further temperature fluctuation may be an increase in temperature.

In another embodiment outputting a signal to generate a notification may comprise illuminating a light source. Outputting a signal to generate a notification may comprise generating a notification on a mobile communication device.

In an embodiment the method may comprise determining a rate of temperature change in the decrease in measured temperature and may further comprise determining when the child is ready to go to sleep when the rate of temperature change exceeds a threshold value.

In one embodiment the method may further comprise determining a fatigue level of the child in dependence on the detected temperature increase followed by the temperature decrease. The fatigue level may be indicative of a behaviour or temperament of the child. The fatigue level may be used to sleep train the child by notifying the parent or carer that the child is fatigued prior to their bedtime.

The invention may further be expressed as a method of predicting when a child is in a state receptive to sleep, the method comprising: measuring a temperature of the child; detecting a fluctuation in the measured temperature of the child; determining when the child is in a state receptive to sleep in dependence on the detected fluctuation in temperature; and outputting a notification when it is determined that the child is in a state receptive to sleep.

The invention may also be expressed as a wearable device for determining a fatigue level of a child, the device comprising: a temperature sensor configured to measure the temperature of the child; and a control module configured to receive the measured temperature of the child from the temperature sensor; wherein the control module is configured to determine, in dependence on a temperature fluctuation in the received measured temperature, the fatigue level of the child; the temperature fluctuation comprising an increase in the measured temperature of the child followed by a drop in the measured temperature of the child; and the control module is further configured to output a notification signal to generate a notification indicative of the fatigue level of the child. Determining the fatigue level of the child is beneficial when sleep training a child. For example, the wearable device may notify a parent that the child is fatigued at a time prior to the child’s bedtime. This allows the parent to take necessary action to calm or relax the child but preventing them falling asleep. For example, the parent may read the child a story until the fatigue level decreases and the child is no longer ready to sleep. This allows the parent to sleep train the child and to instil a regular bedtime routine in the child.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a child wearing a wearable device according to an embodiment of the invention;

Figure 2 is a schematic block diagram of components within the wearable device of Figure 1 ;

Figure 3 is a perspective view of a housing of the wearable device of Figure 1 ;

Figure 4 is a graph showing an example temperature of the child of Figure 1 over a period of twenty minutes;

Figure 5 is a graph showing an example temperature of the child of Figure 1 over a period of fourteen hours;

Figure 6 is a perspective view of a strap of the wearable device; Figure 7 is a cross-sectional view of the housing positioned within an enclosure of the strap;

Figure 8 is a perspective underside view of a lower housing portion of the housing of Figure 3;

Figure 9 is a perspective view of a wearable device according to a further embodiment of the invention;

Figure 10 is an exploded perspective view of the wearable device of Figure 9;

Figure 11 is a perspective view of the underside of the wearable device of Figure 9; and

Figure 12 is a flow chart outlining a method of determining when a child is in a state ready to sleep.

DETAILED DESCRIPTION

In general terms embodiments of the invention relate to a wearable device for determining when a child is ready to go to sleep or when the child is in a state receptive to sleep. The wearable device may be attached to the wrist of a child such that it can measure the temperature of the child. The wearable device may further comprise a processor or control module configured to determine when the child is ready to go to sleep in dependence on a temperature fluctuation detected in the measured temperature of the child. The control module being configured to determine the child is ready to go to sleep when the temperature fluctuation comprises an increase in temperature followed by a drop in temperature of the child. When the control module determines that the child is in a state receptive to sleep a notification signal may be output to generate a notification indicating that the child is ready to sleep. For example, a light on the wearable device may be illuminated, change colour and/ or a notification may be generated on a mobile communication device of a parent or carer.

The wearable device beneficially provides a system to predict when a child is in a state receptive to sleep such that a parent or carer may commence the child’s bedtime routine. Starting the child’s bedtime routine when the child is in a state that is most receptive to sleep advantageously maximises the chances that the child will fall directly to sleep thereby improving the amount of sleep the child receives and also the quality of the sleep the child will receive.

Furthermore, the wearable devices may be worn by the child throughout the day such that temperature of the child is monitored during the day. The wearable device may be configured to determine when the child is tired or when the child is fatigued. This is beneficial when trying to sleep train a child. For example, the wearable device may determine that the child is ready to sleep at 5pm. However, the parent will be aware that the child’s bedtime is not until 7pm and as such the parent may be alerted to the child being ready for sleep before their bedtime. In this instance, the parent may do a relaxing activity with the child until the fatigue or tiredness level of the child passes thereby preventing them from sleeping prior to their bedtime.

To place embodiments of the invention in a suitable context reference will now be made to Figure 1 which shows a schematic view of the wearable device 10 secured to the wrist 14 of an infant or child 12. The wearable device 10 comprises a housing 16 secured to the infant’s wrist via a strap 18. The housing 16 comprises a temperature sensor and control module (not shown in Figure 1) for measuring the temperature of the child 12 such that the wearable device 10 may predict when the child 12 is in a state receptive to sleep. The child 12 may be aged between about six months and five years.

Turning now to Figure 2 there is shown a block diagram of the components within the housing 16 of the wearable device 10. As shown in Figure 2, the housing 16 comprises a temperature sensor 20 for monitoring the temperature of the child 12. The temperature measured by the temperature sensor 20 may be input to a control module 22 or processor. The control module 22 is configured to receive the measured temperature data from the temperature sensor 20 to monitor the temperature of the child 12. When the control module 22 detects a change in temperature or temperature fluctuation indicative of the child 12 being in a state receptive to sleep a notification may be output to alert the parent or carer that the level of fatigue of the child has increased such that the child is ready to go to sleep. The notification may be output by the light source 24. The light source 24 may be activated or change colour to alert a parent or carer that the child 10 is ready to sleep. The wearable device 10 may further comprise a communication module 28 configured to receive a notification signal from the control module 22 and to generate a notification to alert a parent or carer when the control module 22 determines that the child is in a state receptive to sleep. The notification may be in the form of a notification on a mobile communication device 21. The notification output by the notification module 28 may notify the parent or carer that the child 12 is ready to go to sleep such that the parent or carer can start the child’s bedtime routine. This beneficially ensures that the child’s bedtime routine is started when the child 12 is fatigued such that the child is in a state that is receptive to sleeping. The notification may be generated on the mobile communication device 21 in isolation from or in conjunction with a notification on the light source 24. The housing 16 further comprises a power source 26, typically in the form of a battery to provide a source of power to the components within the housing 16.

Turning now to Figure 3 a perspective view of the housing 16 of the wearable device 10 is shown. The housing 16 comprises a lower housing portion 32 and an upper housing portion 34 which can be secured together to form the housing 16. A cavity is defined between the lower and upper housing portions 32, 34 such that the components, for example the temperature sensor 20, control module 22, light source 24, power source 26 and communication module 28 may be located within the housing 16.

The upper housing 34 may comprise a translucent or transparent window 30 such that the light source 24 located within the housing 16 may emit light through the window 30. The light source 24 is coupled to the control module 22 such that when the control module 22 determines that the child is in a state receptive to sleep the light source 24 may change colour or illuminate to alert the parent or carer that the child 12 is ready to sleep.

The colour of light emitted by the light source 24 may vary in dependence on the state of the child 12. For example, when a first temperature fluctuation is detected and it is first determined that the child 12 is in a state ready to sleep the light source 24 may emit a warm white light through the window 30 thereby indicating that the child 12 is ready to go to sleep and that the child’s bedtime routine should be started. As the child’s bedtime routine advances the control module 22 may detect a second temperature fluctuation. The second temperature fluctuation may indicate that the child 12 is about to transition to a state that is less receptive to sleep. If the control module 22 detects a second temperature fluctuation it may output a signal to cause the light source 24 to change to a warm light such as a warm orange light. This is beneficial as the light source 24 provides an indication to the parent or carer that the child 12 should be in their bed at this time and that the child is about to change to a state less receptive to sleep if they are not already in their bed. Furthermore, the warm light may help to relax the child 12 thereby helping the child 12 fall asleep before they transition to a state that is less receptive to sleep.

If the control module 22 subsequently detects a third temperature fluctuation, for example an increase in temperature or an oscillating temperature, indicative of the child 12 still being awake the light source 24 may change to a purple or lilac light to notify to the parent or carer that the child 12 is overtired and that the child 12 is no longer in a state receptive to sleep. The purple or lilac light is beneficial as it provides a subtle colour change which will not draw the attention of the child to the device 10 as doing so may distract the child from going to sleep.

The purple or lilac light may remain illuminated for around thirty to ninety minutes or until the control module 22 detects a temperature fluctuation indicative of the child 12 returning to a state that is receptive to sleep. When the control module 22 detects a further temperature fluctuation indicative of the child transitioning back to being in a state receptive to sleep the light source may again emit a warm white light thereby notifying the parent or carer that the child’s bedtime routine should be started. The skilled reader will understand that the notifications output by the light source 24 may similarly be conveyed to a parent or carer via the mobile communication device 21 .

Figure 4 shows an example of the temperature of a child 12 over a period of twenty minutes in the evening before a child 12 goes to bed. As shown in Figure 4 the temperature of the child 12 starts at 36.4°C which may be considered to be a normal healthy temperature for a child 12. At the start of the time period shown in Figure 4 the child 12 is in a fully awake state and their temperature is considered to be at a normal, healthy level. When the child 12 is about to transition from the fully awake state to a fatigued state or a state receptive to sleep their temperature initially starts to rise at point 70. In the example shown in Figure 4, the child’s temperature climbs from 36.4°C to about 37.3°C over a period of 5 minutes although the period of increase may be up to an hour or more in other examples.

When the child’s temperature peaks at point 72 it then falls sharply at point 74. The temperature fluctuation comprising the initial temperature rise 70, the peak 72 and the subsequent decrease 74 may be considered to be a first temperature fluctuation. The sharp decrease in temperature of the child following a relatively gradual temperature increase is a temperature fluctuation indicative that the child is in a state ready to sleep. The temperature fluctuation is further indicative of a fatigue level of the child 12. When the control module 22 detects a temperature fluctuation comprising a sharp decrease in the child’s temperature the control module 22 may determine that the child 12 is in a state ready to go to sleep or that the child 12 is fatigued. The control module 22 may then output the notification signal to generate a notification by illuminating the light source 24 and/or generating an alert on the mobile communication device 21 .

Following the sharp decrease in temperature of the child 12 the temperature continues to fall for around 5 to 10 minutes before stabilising around 36.4°C at point 76. When the child’s temperature stabilises the control module 22 may determine that the child 12 is about to transition from the state of being ready to go to sleep to an overtired state where the child 12 is less receptive to sleep. The drop in temperature may cause a decrease in temperature to a temperature lower than the temperature of the child prior to the first temperature fluctuation. For example, as shown in Figure 4 the temperature at point 76 may be 36.2°C which is less than the temperature of the child prior to the first fluctuation. In other words, the magnitude of the drop in temperature is greater than the magnitude of the increase in temperature.

The stabilising of the child’s temperature may be considered to be a second temperature fluctuation. When the temperature of the child 12 stops decreasing the child 12 should ideally be settled in their bed and about to go to sleep. Or in the instance when the parent is sleep training the child and the child 12 is deemed to be fatigued at a point that is not suitable for them going to sleep the second temperature fluctuation is indicative of the child 12 beginning to transition out of the fatigued state. At this point 76 the control module 12 may output a second notification signal in response to detecting the second temperature fluctuation. The second notification signal may cause the light source 24 to change colour, for example from a warm white to a warm orange, or for a second notification to be generated on the mobile communication device 21.

The period that the child is in a state ready to go to sleep may last up to about 15 minutes, from the point 74 that the child’s temperature starts to decrease until the point 76 the child’s temperature stabilises. If the child successfully falls asleep the temperature typically stabilises at 36.2°C to 36.6°C at which point the light source 24 may be turned off by the control module 22.

However, as shown in the example temperature data in Figure 4 if the child 12 does not fall asleep the child’s temperature continues to rise and/or oscillate erratically in minutes 15 to 20, at point 78, which indicates that the child 12 has not fallen asleep and has become over-tired meaning they are in a state that is no longer receptive to sleep. If the control module 22 detects a third temperature fluctuation such as a second rise in temperature or an oscillating or erratic temperature a third notification signal may be output such that the light source 24 transitions from the warm orange light to a purple or lilac light and/or the notification on the mobile communication device 21 is updated to alert the parent that the child is overtired and thus is no longer ready to go to sleep. The third temperature fluctuation at point 78 is indicative of a spike in cortisol levels within the child 12 meaning that the child 12 is overtired and no longer in a state receptive to sleep.

The third notification signal generated by the control module 22 beneficially indicates to the parent or carer that the window in which that child 12 was in a state ready to go to sleep has passed and that the child 12 is no longer going to be receptive to sleep. Typically, the temperature of the child will continue to gradually rise or oscillate for around 20 to 30 minutes in this situation before sharply falling at which point the child is deemed by the control module 22 to be ready to go to sleep again. At this point the control module 22 may determine that the child 12 is in a state ready to sleep and generate a notification, for example by emitting a warm white light from the light source 24 to indicate to the parent that the child’s bedtime routine should be started.

Figure 5 shows an example of how a child’s temperature may vary over a fourteen-hour period from 07:00 to 21 :00 on a given day. As shown in Figure 5 the child’s temperature generally varies from around 36.4°C to around 37.1°C over the course of the day. At about 07:00 when the child initially wakes their temperature is about 36.4°C. As the morning progresses the child 12 requires their first nap of the day at around 09:00. When the child 12 is ready to nap a temperature fluctuation 80 is detected. The temperature fluctuation 80 has a relatively sharp increase in temperature followed by a relatively sharp decrease in the temperature. This first temperature fluctuation 80 is then repeated at about 13:00 with a second temperature fluctuation 82 when the child 12 has a second nap.

A third temperature fluctuation 84 is also shown which peaks at 20:00 which is associated with the child 12 going to bed in the evening. The rate of temperature increase associated with the child 12 sleeping in the evening is much lower than the rate of temperature increase associated with the child 12 napping during the day.

The rate of temperature change may also be monitored by the control module 22 to determine when the child 12 is in a state receptive to sleep. As such, the control module 22 may determine if the child is in a state ready to go to sleep based on a temperature fluctuation, the time of day and the rate of temperature change. This is beneficial as the rate of temperature change of the child 12, in particular the rate of the initial temperature increase, may vary depending on the time of day as illustrated in the example shown in Figure 5.

For example, as shown in Figure 5, if the child 12 is about to nap during the day the rate of the temperature increase may be higher than an equivalent increase in the evening before the child’s bedtime. In this scenario, the control module 22 may detect a high rate of temperature increase, for example the first temperature fluctuation 80 or the second temperature fluctuation 82 and if it is during the day the control module 22 may determine that the child 12 is in a state ready to go to sleep when the temperature of the child 12 peaks and starts to decrease again. Similarly, if the control module 22 determines a relatively low rate of temperature increase as shown by the third temperature fluctuation 84 and it is determined that it is in the evening then the control module 22 may determine that the child 12 is ready to go to sleep and output a notification signal accordingly.

The age of the child 12 may also be input into the control module 22 such that the control module 22 may determine an expected amount of sleep the child 12 requires. For example, Figure 5 shows an expected temperature variation for a child 12 having an age of seven to eight months. A child 12 of this age is expected to have around two naps a day where each nap may last around one to two hours. As such, the control module 22 can predict when a child 12 is expected to go to sleep and detect a temperature fluctuation indicative of sleep accordingly. This is beneficial as determining when a child is ready to sleep in dependence on their age, expected sleep pattern and detected temperature fluctuations increases the accuracy of the notifications output by the control module 22.

The skilled reader will understand that the wearable device 10 may be used with children of varying ages and varying sleep requirements. As such, the age of the child 12 may be input to the control module 22 such that the control module 22 can determine how much sleep the child 12 is expected to have. For example, a child 12 of 6 months will require significantly more sleep and daytime naps than a child 12 of two years or older. As such, in cases where the child 12 is not expected to have any daytime naps the control module 22 may not determine, and thus output a notification, that the child 12 is ready to go to sleep in response to a temperature fluctuation detected during the day.

The wearable device 10 may be used as a sleep training aid to determine a fatigue level in the child 12. For example, the wearable device may monitor the skin temperature of the child 12 and determine, in dependence on a detected temperature fluctuation, a fatigue level of the child 12. The fatigue level of the child 12 may be indicative of the child being ready to go to sleep and a notification may be output to the parent or carer. When sleep training the parent may set a target bedtime for the child 12 and if the wearable device 10 determines that the child 12 is ready to go to sleep before the target bedtime a notification may be sent to the parent or carer. The parent or carer may then do an activity with the child such as relaxing or reading them a story to help the child relax when they are tired but stopping them from falling asleep.

Turning now to Figure 6 a perspective view of the top surface of the strap 18 is shown. The strap 18 is configured to secure the housing 16 to a limb of the child 12. For example, the strap 18 may be used to secure the housing 16 to the child’s wrist 14. The strap 18 may be made from a soft plastics material such as silicone. The strap 18 comprises an enclosure 40 for retaining the housing 16. The enclosure 40 is shaped such that the walls of the enclosure 40 surround and encase a substantial portion of the outer surface of the housing 16. This is beneficial as the walls of the enclosure 40 are made from a soft plastics material which the child 12 may chew or bite without damaging their teeth or the housing 16. Furthermore, the enclosure 40 securely retains the housing 16 on the child’s wrist 14.

The strap 18 further comprises two bands 48 extending in opposing directions from the enclosure 40. The bands 48 comprise a fixing or fastening formation (not shown) to secure the bands 48 relative to each other such that the strap 18 may be attached to the child’s wrist 14. The fastening formation may be, for example, a clip, buckle, magnetic fastening or the like. The fastening formation may be adjustable such that the strap 18 may be secured to wrists 14 of varying diameters.

Turning now to Figure 7 a cross-sectional side view of the housing 16 located within the enclosure 40 of the strap 18 is shown. The top surface 42 of the enclosure 40 comprises an aperture 44 for receiving the window 30 of the housing 16. The aperture 44 is dimensioned such that the window 30 is received within and protrudes through the aperture 44, beyond the top surface 42 of the enclosure 40, thereby improving the visibility of the light source 24. The remainder of the housing 16 is encased within the enclosure 40 such that the only portion of the housing 16, apart from the bottom surface 58 of the housing 16, exposed is the window 30. This beneficially ensures the housing 16 is securely fastened to the child’s wrist 14 and the non-skin contacting surfaces of the housing 16 are encased by the enclosure 40.

As shown in Figure 7 the side walls 50 of the enclosure 40 extend up and over the side walls 52 of the housing 16. The top surface 42 of the enclosure 40 extends over the top surface 54 of the housing 16 such that the enclosure 40 encases the housing 16. The enclosure 16 comprises an opening 56 on the underside of the enclosure 40 such that the bottom surface 58 of the housing is exposed. This is advantageous as the bottom surface 58 of the housing 16 may contact the child’s skin in use such that an accurate temperature of the child 12 may be measured. Furthermore, when the strap 18 is secured to the child’s wrist 14 the top surface 42 of the enclosure 40 may engage the top surface 54 of the housing 16 and urge the housing 16 downwardly toward the child’s skin. This is beneficial as it promotes contact between the bottom surface 58 of the housing 16 and the child’s skin thereby improving the reliability of the reading of the child’s temperature. The housing 16 further comprises two tabs 45 located on opposing side walls 52 of the housing 16. The tabs 45 are configured to be located within corresponding engagement slots 47 within the strap 18. The tabs 45 are configured to extend into the engagement slots 47 such that the tabs 45 retain the housing 16 within the enclosure 40. As shown in Figure 7 the tabs 45 extend in a downward direction and the corresponding engagement slots 47 similarly extend in a downward direction. This is beneficial as the downwardly extending tabs 45 act as a barb such that when the housing 16 is located within the enclosure 40 the tabs 45 engage the engagement slots 47. To remove the housing 16 from the enclosure 40 the soft silicone or plastics strap 18 must be elastically deformed to disengage the tabs 45 from the engagement slots 47 thereby preventing the housing 16 being removed by a child 12.

Turning now to Figure 8 a perspective view of the underside of the lower housing portion 32 is shown. The lower housing portion 32 comprises an aperture 60 for receiving the temperature sensor 20. The temperature sensor 20 may extend from within the housing 16 through the aperture 60 such that the temperature sensor 20 may contact the child’s skin. The temperature sensor 20 (not shown in Figure 8) may lie flush with the bottom surface 58 of the housing 16. The aperture 60 may further comprise a circular recess 62 or recessed collar on the bottom surface 58 of the housing 16 for receiving a gasket or seal (not shown). This is beneficial as the seal prevents the ingress of moisture to within the housing 16.

Furthermore, positioning the temperature sensor 20 flush with the bottom surface 58 of the housing 16 beneficially improves the accuracy of the temperature measurements from the temperature sensor 20 by maintaining contact between the temperature sensor 20 and the child’s skin. This in turn improves the detection of temperature fluctuations indicative of the child 12 being in a state receptive to sleep.

The lower housing portion 32 further comprises a charging port 38. The port 38 may comprise a USB connector or the like such that the power source 26 may be charged. The charging port 38 is beneficially located on a side wall 52 of the lower housing portion 32 such that when the housing 16 is located within the enclosure 40 the walls of the enclosure 40 cover and seal the charging port 38. This advantageously prevents the ingress of dirt, moisture or objects into the charging port 38. For example, as a result of the child 12 chewing the wearable device 10 or trying to push an object within the port 38.

Turning now to Figure 9 there is shown a perspective view of the wearable device 10 according to a further embodiment. The strap 18 is configured to secure the housing 16 to a limb of the child 12. For example, the strap 18 may be used to secure the housing 16 to the child’s wrist 14. The strap 18 may be made from a soft plastics material such as silicone or from a fabric material. The strap 18 comprises an enclosure 40 for retaining the housing 16.

As best viewed in Figure 10 the enclosure 40 comprises an opening 90 for receiving the housing 16. The enclosure 40 is dimensioned such that the housing 16 may be at least partially received and retained within the opening 90 of the enclosure 40. The enclosure 40 may be made from a resiliently deformable plastics material such that the housing 16 may be secured by a snap fit within the opening 90 of the enclosure 40. When the housing 16 is located within the opening 90 the enclosure 40 extends around a peripheral edge of the housing 16 and partially extends over and under the upper and lower surfaces of the housing 16 such that the housing 16 is securely gripped within the enclosure 40.

As shown in Figure 11 the enclosure 40 comprises an aperture 92 located at the base of the opening 90 of the enclosure 40. When the housing 16 is located within the enclosure 40 a lower surface 94 of the housing 16 at least partially protrudes through the aperture 92. The lower surface 94 of the housing 16 comprises the temperature sensor 20. Beneficially, as the lower surface 94 of the housing 16 partially protrudes through the aperture 92 the temperature sensor 20 contacts the child’s skin thereby improving the accuracy of the measured temperature of the child 10.

Figure 12 shows a flow chart outlining a method of determining when a child is ready to go to sleep. In Step 101 the temperature of the child 12 is measured. The temperature may be measured by a temperature sensor 20 and the temperature data generated by the temperature sensor 20 may be input to a processor or control module 22 such that the data may be analysed or stored within a memory. In Step 102 the measured temperature is assessed to detect a fluctuation in the measured temperature. The fluctuation in the measured temperature is an increase in the measured temperature followed by a decrease in the measured temperature. In Step 103 the method comprises determining whether the detected fluctuation in the temperature of the child 12 is indicative of the child 12 being in a state receptive to going to sleep. Determining whether the temperature fluctuation is indicative of the child being in a state receptive to sleep may comprise comparing the temperature fluctuation to a temperature fluctuation pattern. The temperature fluctuation pattern may be a pattern selected in dependence on at least one of: the age of the child, the time of day and the child’s previous temperature fluctuations indicative of being in a state receptive to sleep.

Furthermore, the temperature fluctuation may also be indicative of a fatigue level of the child 10. Determining when the child is ready to go to sleep may comprise determining a fatigue level of the child. The fatigue level of the child may be indicative of the behaviour of the child. For example, if it is determined that the fatigue level is increasing as a result of a detected temperature fluctuation then the child may become more prone to tantrums or periods of being over-tired.

In Step 104, when it is determined that the child 12 is in a state ready to go to sleep a notification signal is output to generate a notification. The method may further comprise monitoring the child’s temperature and determining when the child is no longer in a state receptive to sleep in dependence on the monitored temperature. For example, if the child’s temperature stabilises it may be indicative of the child 12 having fallen asleep. Alternatively, if the child’s temperature continues to fluctuate, for example rise, it may be determined that the child is no longer in a state receptive to going to sleep.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.