The invention relates to an alarm peripheral, in particular to a camera or a glass break sensor.

Alarm peripherals are used in security systems in the private or industrial sector for monitoring an apartment, a house, office space within a building, an entire building, or the like. They are designed to detect an unwanted intrusion into an area, which is under surveillance.

An alarm system installation typically comprises a central unit and one or more peripherals. The central unit is typically mains-powered and serves for external communication, e.g. for sending an alarm call to an external operation centre. The peripherals communicate with the central unit and can, amongst other things, be sensors, cameras or communication interfaces via which a user can communicate with the central unit, e.g. to arm or disarm the alarm system installation. The peripherals and the central unit may communicate using wired links, but in many situations, wireless communication is preferred.

Battery power is often used in preference to other types of power supply, such as a networked “mains” power supply or an intermittent or unreliable one such as solar, wave or wind, where continuity of supply is required together with a freedom to locate the device being powered without the constraint of having a wired connection. For example, in security monitoring systems, such as domestic burglar alarms and the like, peripherals such as glass-break detectors, movement sensors, door/window sensors, video cameras, and microphones, are preferably battery- powered so they can be situated wherever is most appropriate or most convenient without the need to run an electrical supply line. A problem with battery power is that, unlike “mains” electricity, the amount of power available is limited, so that eventually the batteries need to be replaced before they are completely exhausted, to avoid the peripheral from ceasing to operate. Obviously, the proper operation of a security monitoring system is critically dependent upon the proper functioning of the various peripherals of the system. For security monitoring and alarm systems, particular when installed to protect domestic or small-business premises, camera peripherals are usually installed to capture images only when triggered, rather than continuously. In such applications, it is generally preferred to use battery rather than mains power, but it can then be a problem to achieve a satisfactorily long battery life. The desires to have compact peripherals, that don’t weigh too much, together with the desire to reduce battery cost all push towards constraining the physical size of the battery, but the desire for a battery life of several years, preferably as much as 5 years, encourages the use of batteries with higher charge capacity. At the design stage, decisions are made about the energy storage capacity required of a battery pack to achieve a desired minimum battery life, suitable battery chemistries, and in turn the size of the battery compartment needed to house the battery pack.

Of course, the battery life actually achieved with any peripheral depends significantly on the peripheral’s duty cycle, in the case of a camera, how often the peripheral is activated to capture images and to send them to the central unit of an alarm or monitoring system. For many installations, where a camera is unlikely to be triggered except in the event of an intrusion, it may be possible to achieve the target battery lifetime with a set of disposable batteries such as lithium ion batteries (for example, a set of lithium ion AA batteries). Whereas, in some other installations a camera peripheral may be expected to be triggered much more frequently, so that an acceptable battery lifetime is unlikely to be achieved using a similar set of batteries. In such a situation, it may just be accepted that the battery pack will need to be changed more frequently and, in that case, rechargeable batteries used instead of disposable batteries, battery packs being swapped and recharged periodically.

The effective lifetime of a battery pack of a peripheral can be increased by providing a photovoltaic arrangement configured to charge the battery pack, even though the photovoltaic arrangement may be unable to supply sufficient current to fully power the peripheral. For example, the peripheral may include a first radio transceiver, that consumes little power, for periodic communication of control signals and the like with a central unit of the alarm system installation, and a second radio transceiver for transmitting data, such as images or video signals, that consumes significantly more power: the first radio transceiver may be an 868MHz ISM device, and the second transceiver may be a Wi-Fi transceiver. The photovoltaic arrangement may provide sufficient power to be able to satisfy the energy demands of the first radio transceiver in communicating with the central unit, but may not provide sufficient power to be able to satisfy the energy demands of the second radio transceiver when transmitting video files or video streams via Wi-Fi, for example.

It is also known to use fire detectors to detect a fire in an area under surveillance. To this end, various devices and methods are known. One type of fire detection device is a point heat detector which detects a fire based on temperature. Another approach for detecting a fire is based on the detection of the smoke which is produced by a fire. This can be done be detecting the smoke as such by means of a suitable sensor, or by detecting the decrease in the visibility which that occurs as a consequence of the smoke which is being produced. A still further approach for fire detection is the detection of the electromagnetic radiation emitted from the flames. This approach is based on the fact that flames emit light in a certain wavelength in a range which differs from the wavelength of daylight or LED light, for example.

The disadvantage of these devices is that some are very complex and difficult to integrate into other systems.

Therefore, it is the object of the invention to provide a simple device and method for fire detection.

This object is solved by an alarm peripheral having a sensor, an energy storage device, a photovoltaic cell and a control unit, the control unit having a fire detection module adapted for detecting voltage pulsations in the output signal of the photovoltaic cell, which are characteristic for a fire, and for generating a fire alarm. This object is also solved with a method for fire detection by means of an alarm peripheral, the alarm peripheral having a photovoltaic cell, the method comprising the steps of having a fire detection module identify a flickering characteristic of the output signal of the photovoltaic cell, having the fire detection module identify an increase of the output signal of the photovoltaic cell, emit a fire alarm signal if both the flickering characteristic and the increase of the output signal are present.

The invention is based on the recognition that fire emits a flickering light and on the idea to use, for fire detection, a photovoltaic cell, which is provided anyhow for charging an energy storage of the alarm peripheral.

Because of a fire emitting a flickering light, a photovoltaic cell exposed to the light of the fire generates an output signal that has a flickering characteristic. The presence of the flickering characteristic in the output of the photovoltaic cell is a reliable indicator for the presence of a fire. Other sources of radiation of light received by the photovoltaic cell do not have a flickering intensity. A lamp provides a constant light, which results in a corresponding constant output signal (voltage or current). A sunrise or sunset leads to a steadily increasing or decreasing output signal. A temporary obscuration of the photovoltaic cell results in a sudden drop in the voltage signal (and possibly in an ensuing increase back to the previous level). It is only a fire which has a flickering characteristic.

It has been found out that even the light (and the corresponding flickering characteristic) from such a weak light source as a candle can be detected. It is thus advantageous to base the decision whether or not a fire alarm should be emitted, not only on the detectable flickering characteristic, but to further take into account an increase in the intensity of the output signal of the photovoltaic cell. An uncontrolled fire results in an increase of the output power of the photovoltaic cell (in addition to the flickering characteristic) which warrants a fire alarm while a candle does not involve an increase in the output power of the photovoltaic cell. Thus, false fire alarms (which would disturb a candle light dinner or other similar situations) are prevented.

Preferably, the photovoltaic cell is a highly sensitive photovoltaic cell for indoor application. Such photovoltaic cells are preferred for alarm peripherals as they allow charging the energy storage device with the light from a lamp so that the alarm peripheral does not have to be placed so as to be exposed to daylight. In addition, the low sensitivity of the photovoltaic cell allows detecting a fire at a very early stage. The photovoltaic cell can in particular be a dye sensitized photovoltaic cell or an organic photovoltaic cell which can harvest energy with a very low lux level.

In an embodiment of the invention, the alarm peripheral is a camera or a glass break sensor or comprises a camera and/or a glass break sensor. This allows easily integrating a fire alarm function into a known safety device.

Preferably, the energy storage device is a battery or an accumulator or a supercapacitor. Preferably, the energy storage device is rechargeable.

Preferably, the photovoltaic cell is configured to charge the energy storage device with electrical energy and/or to provide power for the alarm peripheral.

For example, the photovoltaic cell is configured to charge the energy storage device while the energy storage device is coupled for providing energy for the alarm peripheral. Thus, the photovoltaic cell has a double function which allows a particularly compact and cost efficient design of the alarm peripheral.

In particular, the photovoltaic cell is configured for charging the energy storage device and detecting a fire at the same time.

According to one embodiment, the alarm peripheral comprises a movement sensor. For example, the movement sensor is an ultrasonic-based movement detector. The movement sensor is configured for detecting intruders.

The alarm peripheral may comprise a housing, wherein the photocell and/or the movement sensor and/or the camera and/or the glass break sensor are accommodated by the housing, for example in and/or on the housing. This also contributes to a compact design of the alarm peripheral.

According to one embodiment of the alarm peripheral, the alarm peripheral comprises a camera or is a camera, wherein the alarm peripheral is configured to operate in a low power consumption mode in which the camera is not activated and a high power consumption mode in which the camera is activated, wherein the control unit is configured to switch the alarm peripheral from the low power consumption mode to the high power consumption mode in response to detection of voltage pulsations characteristic of a fire for capturing a visual image. Thereby, the energy consumption of the alarm peripheral can be kept low. In particular, a power intensive image capture and/or recording mode of the camera is only activated when a critical situation is suspected.

Preferably, the fire detection module identifies a flickering characteristic of the output voltage of the photovoltaic cell. While it is also possible to analyze the output current of the photovoltaic cell, it has been found out that analyzing the output voltage is the simplest and most reliable solution.

The fire detection module can use fluctuations of as low as ±0.05 V in the output voltage of the photovoltaic cell for making a determination whether or not a flickering characteristic of the output voltage is present. With this high sensitivity, a fire can be detected at a very early stage.

Preferably, the fire detection module identifies an increase of the output voltage over a certain period of time, the period of time being at least in a range of 15 s. This allows a distinction between a short-term increase for reasons other than an uncontrolled fire on the one hand and an increase which is typical for an uncontrolled fire for which a fire alarm should be generated.

According to one embodiment of the method, the alarm peripheral is or comprises a camera, wherein the alarm peripheral and/or the camera is switched from a low-power consumption mode to a high-power consumption mode upon detection of a fire by the fire detection module and/or optionally upon detection of an intrusion by a movement sensor, if provided.

In the following, the invention is explained by reference to the enclosed drawings. In the drawings:

Fig.1 is a schematic representation of the alarm peripheral,

Fig. 2 schematically shows a first embodiment of an energy storage device with a cover and a photovoltaic cell,

Fig. 3 schematically shows a second embodiment of an energy storage device with a cover and a photovoltaic cell,

Fig. 4 shows a diagram of output voltage over time that is characteristic for a lamp,

Fig. 5 is a diagram of output voltage over time that is characteristic for a sunrise, Fig. 6 shows a diagram of output voltage over time that is characteristic of a candle,

Fig. 7 is a diagram of output voltage over time that is characteristic for an obscuration of the photovoltaic cell,

Fig. 8 shows a diagram of output voltage over time that is characteristic of a light source that is obscured repeatedly, and

Fig. 9 is a diagram of output voltage over time that is characteristic of an uncontrolled fire.

Fig. 1 schematically shows an alarm peripheral 10. It is being used in security systems in the private or industrial sector for monitoring an apartment, a house, office space, an entire building, or the like.

The alarm peripheral 10 is designed to detect an unwanted intrusion into an area which is under surveillance. The alarm peripheral 10 can be any security or monitoring device. Preferably, it is a security camera or a movement detector or a glass break sensor or a combination of any of these, such as those used in security systems for houses, apartments or office buildings, wherein the alarm peripheral 10 can be placed inside or outside of a building.

The alarm peripheral 10 includes a sensor 12, an energy storage device 14, a photovoltaic cell 16 and a control unit 18. The control unit 18 includes a fire detection module 20.

In addition, the alarm peripheral 10 can include a movement sensor 21 , for example an ultrasonic-based movement detector. The movement sensor 21 may be used as, or in combination with, the sensor 10.

Depending on the application, the sensor 12 can be attached to the alarm peripheral 10 or integrated into the alarm peripheral 10. Different types of sensors can be used. Sensor 12 can be a CCD in case the alarm peripheral 10 is a camera. For example, a camera uses an optical sensor while a glass break sensor uses a shock sensor that detects vibrations. Such vibrations can for example occur when a window is smashed. Depending on the design of the device, it is possible to use other types of sensors or to combine them. In a further embodiment, the alarm peripheral 10 may comprise a camera and a glass break sensor.

The energy storage device 14, the photovoltaic cell 16, the movement sensor 21 and the control unit 18 and optionally the sensor 12 are accommodated in and/or on a common housing 24. The housing 24 may include a cover 22 described below.

Energy storage device 14 can be a battery or accumulator that can store electrical energy and supply electrical energy to the components of the alarm peripheral 10. Hereafter, any reference to a battery should, unless the context clearly requires otherwise, be taken also to include other energy storage devices and arrangements, such as capacitors. Similarly, references to a battery compartment or the like should be taken to embrace compartments to house any other power storage device. Howsoever implemented, the energy storage device 14 may optionally be rechargeable in use.

Photovoltaic cell 16 is preferably a very sensitive solar cell suitable for indoor use. It can be e.g. a dye sensitized solar cell or an organic photovoltaic cell which can harvest energy with a very low lux level. By using such a photovoltaic cell 16, it is possible to use the alarm peripheral 10 not only for outdoor applications but also for indoor applications where alarm peripheral 10 is not exposed to direct daylight.

Current supplied by the photovoltaic cell 16 may be sufficient to compensate for energy used during normal operation of a device for example, for a camera peripheral of a security monitoring system, the current supplied may be enough to compensate, or largely to compensate for the energy used for periodic radio checks with the central unit of the security monitoring system, thereby leaving more energy to be used to handle alarm events and the streaming of images or videos over a wireless link.

The photovoltaic cell 16 may be provided on an outer surface of a cover 22 or in the form of a cover 22 for a compartment within the energy storage device 14, which is preferably convex. Optionally, the cover 22 is in the form of a hemicylinder (Fig 2 and 3). By giving the cover 22 a convex, e.g. hemicyhndncal, shape, the photovoltaic cell 16 may more effectively gather sunlight even when mounted on (in the Northern Hemisphere) a North-facing wall. In this way, the photovoltaic cell 16 may provide power more reliably than would be the case with a poorly aligned flat panel arrangement. The curved shape of the photovoltaic cell 16, which may adhere closely to the cover 22, is also less likely to act like a sail when caught by the wind, shedding the wind rather than generating force likely to disturb anti tamper sensors within the alarm peripheral 10 or, in a worst case scenario, to rip the camera from whatever it is mounted on.

Optionally, in use, an energy storage device 14 within the battery housing is at least partly received within the cover 22. In other words, the cover 22 has a II- shaped cross-section with two legs, whereby the energy storage device 14 is arranged between the two legs and has a convex shape on one side. The II- shaped cover 22 thus is arranged like a cap on the convex side of the energy storage device 14.

The photovoltaic cell 16 is optionally flexible.

In an alternative configuration, the photovoltaic cell 16 may be inflexible but may still be arranged to conform to the exterior form of the alarm peripheral 10.

In an alternative configuration, the photovoltaic cell 16 may be provided in the form of a flat planar panel, rather than as one that wraps around the body of the alarm peripheral 10, as shown in Fig. 2 and 3. For example, the cover 22 may include an external face upon which is affixed a planar photovoltaic cell 16. With such an arrangement, care is preferably taken when installing the alarm peripheral 10 to ensure that the photovoltaic cell 16 is so arranged that it is in use sufficiently exposed to the sun or other relevant light source to be able to generate a useful amount of power.

Preferably, the photovoltaic cell 16 produces in the region of 75-150 mW under conditions of bright sunlight, for example in the range 80 to 120mW, possibly 80 to 100mW.

The cover 22 may further comprise electronics to adapt an output of the photovoltaic cell 16 to a suitable form for supply to the energy storage device 14, which can be a rechargeable battery pack. The electronics configured to adapt an output of the photovoltaic cell 16 may comprise a voltage converter.

The rechargeable battery pack may, where the alarm peripheral 10 is a video camera, have a capacity of 30 to 50Wh, for example between 35 and 45Wh, and optionally between 40 and 45 Wh. For other applications, the battery capacity will often be smaller, and yet other applications may use battery packs of greater capacity. Other alarm peripherals, for example glass break detectors, typically have much lower maximum energy requirements, so that for them lower capacity, and possibly much lower battery capacities, will typically be used.

Electrical contacts on the rechargeable battery pack may provide a first interface through which a first electrical interface of the alarm peripheral 10 draws current. A charging interface may be provided on the cover 22, which in use couples with and provides electrical current to a second corresponding interface on the rechargeable battery pack. The charging interface may for example be in the form of a male micro USB plug, to mate with a corresponding socket in the rechargeable battery pack, although it will be appreciated that other types of interfaces and in particular other plug/socket combinations may be provided where appropriate.

Between the photovoltaic cell 16 and cover’s charging interface electronics may be provided to adapt an output of the photovoltaic cell 16 to a suitable form for supply to the rechargeable battery pack. The electronics to adapt an output of the photovoltaic cell 16 to a suitable form for supply to the rechargeable battery pack may comprise a voltage converter.

The rechargeable battery pack may, rather than being in the form of a readily interchangeable battery pack, be integrated into the body of the alarm peripheral 10 in effect, integrated into the battery housing. This may enable a more compact configuration, by eliminating the requirement to provide a protective outer body as part of the battery pack. The rechargeable battery pack could simply be hard wired into the alarm peripheral 10, and an interface provided for connection to a photovoltaic cell 16.

Control unit 18 controls the general functions of alarm peripheral 10. It particularly controls sensor 12 and the communication with a central alarm unit (not shown here) which processes the information provided by alarm peripheral 10. Further, control unit 18 controls charging of energy storage device 14.

Fire detection module 20 can be implemented as a physically separate unit or can be integrated into control unit 18. It is adapted for detecting an uncontrolled fire and for generating a fire alarm.

Fire detection module 20 is arranged to evaluate the output signal of photovoltaic cell 16. As an example, fire detection module 20 receives the output voltage which is being generated when photovoltaic cell 16 is exposed to light, and is adapted for recognizing whether or not the output signal has a flickering characteristic.

A “flickering characteristic” here designates a repeated, quickly occurring change of the signal around a medium value. The amplitude of the flickering can be as low as ± 0.05V in an example where the voltage is monitored, and the “frequency” of the flickering is above 1 Hz.

Fire detection module 20 is further adapted for determining whether or not the output signal of photovoltaic cell 16 increases over a relevant period of time. An increase of the output signal over a relevant period of time here means an increase in either the voltage, the current, or both the voltage and the current, over a time period which is at least 5 seconds and preferably more than 15 seconds.

Figure 4 shows a diagram of the output voltage of photovoltaic cell 16 over time in a case where photovoltaic cell 16 is exposed to the light generated by a lamp. The output voltage is constant. Fire detection module 20 will neither detect a flickering characteristic nor an increase of the output signal.

Figure 5 shows a diagram of the output voltage of photovoltaic cell 16 over time in a case where photovoltaic cell 16 is exposed to indirect light in a room during sunrise. The output voltage increases so that fire detection module 20 will detect an increase in the output signal of photovoltaic cell 16. Fire detection module 20 will however not detect a flickering characteristic in the output signal.

Figure 6 shows a diagram of the output voltage of photovoltaic cell 16 over time in a case where photovoltaic cell 16 is exposed to the light of a candle or of a fireplace. The output voltage has a flickering characteristic which is being detected by fire detection module 20. Fire detection module 20 will however not detect an increase in the output signal of photovoltaic cell 16.

Figure 7 shows a diagram of the output voltage of photovoltaic cell 16 over time in a case where photovoltaic cell 16 is temporarily obscured, for example by a person standing between a lamp and photovoltaic cell 16. The output voltage temporarily drops. The drop however does not qualify as a flickering characteristic, and there is no general increase in the output signal. Thus, fire detection module 20 will detect neither a flickering characteristic nor an increase of the output signal.

Figure 8 shows a diagram of the output voltage of photovoltaic cell 16 over time in a case where the light falling into a room is repeatedly interrupted, for example because of the branches of a tree moving in the wind. The output voltage repeatedly changes between a low value and a high value. The frequency of the change however is quite low, and there is not general increase in the output signal. Thus, fire detection module 20 will detect neither a flickering characteristic nor an increase of the output signal.

Figure 9 finally shows a diagram of the output voltage of photovoltaic cell 16 over time in a case where photovoltaic cell 16 is exposed to the light of an uncontrolled fire. The output voltage very quickly changes between a lower and a higher value, with the amplitude being possibly as low as ±0.05V. Further, the output voltage generally increases. Thus, fire detection module 20 detects a flickering characteristic and in addition an increase of the output signal.

In order to avoid that it is a random short-time increase for reasons other than an uncontrolled fire, this increase in the output voltage intensity is detected over a certain period of time with a minimum duration. The minimum duration is e.g. 15 seconds. Depending on the application, the minimum duration can also be e.g. 30 seconds or 1 minute.

The combination of a flickering characteristic and an increase of the output signal over a significantly long period of time is interpreted as an indication that an uncontrolled fire exists. Thus, control unit 18 generates a fire alarm which will be transmitted to the central alarm unit. Further, an alarm sound can be generated directly by alarm peripheral 10. In case that the alarm peripheral 10 is a camera or comprises a camera, the alarm peripheral and/or the camera can be operated in two different modes, in particular in a low-power consumption mode and a high-power consumption mode.

In the low-power mode, a fire detection algorithm is operative, but the camera is not in operation, which means that the camera does not record or send images. However, the camera may be in a standby mode in order to be able to receive signals from the control unit 18.

In the high-power mode, the camera is activated in response to a signal, for example from the control unit 18.

According to one option, the control unit 18 automatically sends a signal to activate the camera in response to an alarm or a suspicion trigger in order to generate an image or video stream to enable verification of a suspected fire and/or intrusion situation, if appropriate. In particular, the control unit 18 activates the camera when the detection module 20 detects a fire and/or the movement sensor 21 , if provided, detects a movement.

In another option, the camera can be activated manually by a user. For example, the control unit 18 can send a message to a mobile terminal of a user upon detection of a suspected fire or intrusion situation and the user can send an according signal to the control unit 18 to activate the camera.

According to a further option, the camera can be activated automatically or manually by a central monitoring station.

The alarm peripheral 10 may comprise an image processing unit 26 which is configured for analysing the images or videos recorded by the camera in the high- power mode. In particular, the image processing unit 26 is configured to evaluate if a fire or intrusion situation has occurred.

In order to evaluate if a fire or intrusion situation has occurred, comparative images or videos are stored in the image processing unit 26.

If the image processing unit 26 discovers that the alarm is a false alarm, the camera goes back to the low-power mode. Additionally or alternatively, the images or videos recorded by the camera can be send to a central monitoring station or to a mobile terminal of a user and the user can confirm that a critical situation is present or, if the user decides that the situation is not critical, send the camera back to the low-power mode.