WO2018054990A1

WO2018054990A1 - A stand-alone overheat detection alarm device

Info

Publication number: WO2018054990A1
Application number: PCT/EP2017/073803
Authority: WO
Inventors: Seán Ó'TUAMA; Pranay PODDER
Original assignee: Firemole Limited
Priority date: 2016-09-22
Filing date: 2017-09-20
Publication date: 2018-03-29

Abstract

An alarm device (1) is for adhering in a convenient manner on an object such as a phone charger. The device is stand-along having its own independent power supply, requiring no mechanical or electrical connection to the object being monitored, the only interface being that it adheres to the object. It has a housing having a shell (2) over a base (6) to be adhered (4) to an object and to provide a thermal path in which there is a temperature sensor (12, 13). A processor (11) is linked with the temperature sensor and is configured to generate an alert if temperature above a threshold is detected. A sounder (14) is activated if the temperature rises to a level which could cause a fire risk.

Description

"A Stand-alone Overheat Detection Alarm Device"

Introduction The invention relates to fire safety.

There are unfortunately a considerable number of serious fires annually arising from electronic and electrical devices and equipment over-heating. Major examples are phone, tablet and laptop chargers, fryers, portable battery chargers, and electrical leads.

There has been an increasing number of cases whereby fires have been caused by charging devices.

Habitually, chargers or charging devices are often plugged in to charge a device overnight. This can often mean that the device is left unattended for long periods of time and electronically connected for a longer period of time than necessary, resulting in an increased risk of the device overheating.

The use of generic charging devices has further increased this risk. Generic chargers on auction sites are considerably cheaper than their branded counterparts but with no guarantee they meet relevant safety standards.

Furthermore, generic chargers are often advertised as being compatible with many devices. However different devices require different levels of charge, and so generic chargers run the risk of putting too much energy into a device, thus causing the battery to overheat.

For these reasons, the use of charging devices has resulted in a considerable amount of fires occurring in homes. (Reference: http://www.bbc.com/news/uk-27390466). The invention addresses this problem. - -

Summary of the Invention

We describe an alarm device comprising:

a housing having a shell and a thermally conductive base and being arranged to be adhered to an object to provide a thermal path from an object, said housing containing;

a temperature sensor;

a processor linked with the temperature sensor and being configured to generate an alert if temperature above an alert threshold is detected, and an output means for communicating an alert; and

a battery providing power to the device,

The base may include a resilient portion for conformity with a curved object surface. The resilient portion may include a resilient pad. The adhesive pad may comprise double-sided adhesive tape. The base may comprise a metal plate.

Preferably, the base includes a raised platform. Preferably, the base comprises opposing hooks engaging the shell. Preferably, the shell comprises opposing slots for receiving the hooks of the base. Preferably, the base and the shell are flexible enough to allow snap-fitting of the hooks into the slots.

The temperature sensor may include a component which is mounted in an aperture of a substrate supporting the temperature sensor. Preferably, the temperature sensor is mounted to be in contact with the base. Preferably, the aperture is in a circuit board within the housing, said circuit board supporting the temperature sensor and the processor. Preferably, the substrate aperture includes a thermally-conductive compound physically retaining the temperature sensor component in the housing, but allowing transfer of heat to the component.

The temperature sensor may include a transducer having a resistance which varies with temperature, and a reference transducer which is outside of a heat transfer path within the housing. Preferably, said reference transducer is mounted on a circuit board on a side of said board opposed to the base. - -

Preferably, the housing includes at least one domed portion having a depth which is less than 50% of a maximum width dimension. Preferably, the depth is less than 40% of the width dimension and the area of the base is in the range of 400 mm 2" to 2000mm 2". Preferably, the device depth is in the range of 7 mm to 12 mm, and its maximum lateral dimension is in the range of 40 mm to 55 mm. The housing may have a configuration of overlapping domes. This provides a distinctive shape, allowing easy recognition of the fact that a device is in place on an object. Preferably, the housing has a top surface suitable for display of indicia. This may be important for safety information, for example.

Preferably, the output means includes one or more selected from:

an audio sounder,

a light emitter such as an LED,

a vibratory device, and

a wireless communication interface.

Preferably, the device includes a test and/or silence button and the processor has a corresponding test and/or silence function. Preferably, the test and/or silence button (16) is located to be accessed by a narrow tool via an aperture (9) in the housing.

Preferably, the battery is rechargeable and the device comprises an energy harvester and a power management module for charging the battery. Preferably, the energy harvesting module is a thermal energy harvesting module having a hot surface facing the base, and an opposed cold surface and is configured for generating an electrical charge arising from temperature difference between the hot and cold surfaces.

Preferably, the thermal energy harvesting module hot surface is mounted in contact with the thermally conductive base. Preferably, the thermal energy harvesting module is housed between the circuit board and the thermally conductive base.

Preferably, the thermal energy harvesting module is housed within a raised platform of the thermally conductive base. - -

Preferably, the thermal energy harvester is in a thermal path which is separate from a thermal path to the temperature sensor. Preferably, the thermal energy harvester is alongside the temperature sensor. The power management module may be configured for stepping up the voltage received from the thermal harvesting module.

Preferably, the device further comprises a thermally-activated switch for activating components of the device only when an activation temperature of the base is detected. Preferably, the thermally- activated switch is physically located in contact with the base.

Preferably, the device comprises a thermal energy harvester linked with a rechargeable battery, and the thermally- activated switch is located between a power management module and the controller.

Preferably, the housing comprises at least four vents for temperature equilibrium with ambient.

Additional Statements According to the invention there is provided an alarm device comprising:

a housing having a base arranged to be mounted to an object and to provide a thermal path;

a temperature sensor mounted in said thermal path;

a processor linked with the temperature sensor and being configured to generate an alert if temperature above or below a threshold is detected, and

an output means for communicating an alert.

In one embodiment, the housing is configured for securing to a heat- generating object such as a domestic plug or appliance charger, and the processor is configured to detect rise of temperature above a maximum alarm threshold. In one embodiment, the base is arranged to be adhered to an object. - -

In one embodiment, the base includes a resilient portion for conformity with a curved object surface. In one embodiment, the base comprises a plate forming part of the housing and an adhesive pad for contacting an object.

In one embodiment, the adhesive pad comprises double-sided adhesive tape. In one embodiment, the base includes a metal plate.

In one embodiment, the temperature sensor includes a component which is mounted in an aperture forming part of said thermal path.

In one embodiment, the aperture is in a circuit board within the housing. In one embodiment, the aperture is a through-hole.

In one embodiment, the through hole includes a thermally-conductive compound physically retaining the temperature sensor component in the housing, but allowing transfer of heat to the component.

In one embodiment, the housing has a top surface suitable for display of indicia.

In one embodiment, the housing is flexible to allow conformity with a curved object surface profile.

In one embodiment, the temperature sensor includes a transducer having a resistance which varies with temperature. In one embodiment, the temperature sensor includes a reference transducer which is physically spaced apart from said heat transfer path.

In one embodiment, said reference transducer is mounted on a circuit board on a side of said board opposed to the base.

In one embodiment, the output means includes one or more selected from:

an audio sounder,

a light emitter such as an LED,

a vibratory device,

a signal communication interface, preferably a wireless interface. - -

In one embodiment, the device includes a test and/or silence button and the processor has a corresponding test and/or silence function. Detailed Description of the Invention

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which :-

Fig. 1 is a perspective view of an alarm device of the invention in use on a plug adapter;

Fig. 2 is a perspective view of the alarm device in use on a transformer; Figs. 3(a) and 3(b) are top perspective views of the device from different angles, and Fig.

3(c) is a bottom perspective showing the underneath of the device;

Figs. 4(a) and 4(b) are exploded views from above of the device, and Fig. 4(c) is an exploded view from underneath;

Fig. 5 is a plan view showing internal components of the device on a circuit board;

Fig. 6 is a cross-sectional view of the device in the direction of the arrows VI- VI of Fig. 5;

Fig. 7 is a perspective view of an alternative device, which includes an energy harvester, and Figs. 8 and 9 are a physical layout diagram and an electrical schematic respectively;

Fig. 10 is a perspective view of top side internal components of the device of Figs. 7 to 9;

Fig. 11 is an underneath perspective view of internal components of the device;

Fig. 12 is a sectional view of the device in the longitudinal direction, including the housing, Fig. 13 is a cross-sectional view of the device; and - -

Figs. 14 and 15 are perspective and side view images showing a thermal simulation of the device in operation.

Device 1

Referring to the drawings an alarm device 1 of the invention comprises a housing 2 with a shell 3 having a low-profile shape with two overlapping domes. The housing shell 2 is made up of a smaller dome 2(a) and an overlapping (as viewed in the front view) larger dome 2(b) to house the battery B. Fig. 1 shows the device 1 attached to a typical plug adapter P. The device 1 adheres to the plug P, and a test/silence button is accessible through an aperture 9 in the shell by use of a pointed object such as a writing pen. Fig. 2 shows the device 1 on a transformer T from which extends a power lead L. The shape of the housing is optimum for fitting of the device over an electrical device such as a phone charger. The device is low profile, with a depth of about 9mm and this dimension is preferably in the range of 7 mm to 12 mm, and a length of approximately 46 mm and this dimension is preferably in the range of 40 mm to 55 mm. The maximum width dimension is about 37mm and this dimension is preferably in the range of 20 mm to 40mm. The domed portions have a depth which is less than 50% of a maximum width dimension. The depth to length ratio of the device is approximately 1:5. The area of the base (6) is preferably in the range of 400 mm² to 2000 mm².

The device 1 adheres to the object being monitored by double sided thermal tape 4. This provides reliable adhesion to the object, and also provides a degree of flexibility so that there is a good extent of surface area of contact even if the surface of the object being monitored is curved with a shallow profile.

Advantageously, the device has an independent power source in the form of a battery B. Therefore there is no need for an external electrical connection to power the device, and no external cables. All that is required is that the user applies the device to the object being monitored, without need to make any connections. - -

As can be seen in Figs. 1 and 2, the device has been designed such that the widest point does not extend beyond a typical plug adapter P and is low profile relative to the adapter P. Due to this design, the device does not protrude unnecessarily from the adapter. Because of this, the risk of the device being accidently knocked off the plug or adapter is reduced. The device also has smooth edges so as to not have sharp corners, and so the device is difficult to remove from a plug or adapter. This is of particular benefit when the device is to be used with a children's device charger.

Figs. 3(a), 3(b) and 3(c) show the device in more detail. The device housing 2 comprises a base plate 6 with a raised platform 7 to which is adhered an adhesive pad 4. The platform 7 is raised approximately 1mm from the base plate 6, however in other embodiments this may be greater. The 1mm stand-off 7 in the base 6 ensures that the plastics shell 2 is not obstructing the metal base 6 from adhering correctly to the monitored unit. The stand-off 7 helps to ensure that the exposed adhesive surface is proud of the shell 2 and so completely adheres to an object such as a plug adapter P. Also, it provides additional strength to the device.

The adhesive means may be an adhesive pad or thermal tape 4, and may in general be any substrate which is flexible and resilient such as a foam pad. The base plate 6 also comprises opposed hooks 20 and 21 for inserting into slots 22 and 23 respectively of the shell 2 in a snap-fitting manner. The hook 20/21 and slot 22/23 connection provides the connection between the shell 2 and the base 6. This allows for assembly and disassembly of the device, without the need for tools other than a flat-headed screwdriver or a knife edge, while also being difficult for children to open. In general, users will only need to open the device after a considerable period, to replace a battery B.

The adhesive pad 4 is replaceable and may be a double sided thermal tape 4. This replaceability is achieved without need to open the device. Figs. 4(a), 4(b) and 4(c) are exploded views of the device showing that the device 1 comprises a circuit board 8 mounted within the housing 2. The circuit board 8 supports the following components:

11 , microproces sor (U 1 ) ; - -

12, resistor (R12) forming part of a temperatures sensor;

13, aperture mounted thermistor (R13) also forming part of the overall temperature sensor;

14, alarm sounder;

15 , battery holder having a battery B ;

16, test/silence button accessible by the user via the housing shell aperture 9.

The battery holder 15 is an enclosure which almost completely covers the "coin" battery B. This allows for easy removal for an adult, but is difficult for a child even in the highly unlikely event that the child were able to open the housing. The components R12 and R13 are a resistor and thermistor sensor working together to form the temperature sensor.

The mounting of the thermistor 13 is shown most clearly in Figs. 5 and 6. It is connected to the board 10 by positive and negative legs using solder. The thermistor 13 penetrates through a hole 26 in the centre of the circuit board 10. The thermistor 13 is in contact with the internal surface of the conductive base 6. This means that the thermistor 13 can detect heat conducted by the base 6 through a thermal path including the adhesive pad 5 and the metal base 6.

The resistor 12 and the thermistor 13 work together as voltage dividers, in which the resistor 12 is connected to ground and the thermistor 13 is supplied from the processor 11 Ul-Pin5. The resistance of R13 varies with temperature which also shifts the voltage level between R12 and R13 which is measured on Ul-Pin6. The microprocessor 11 (Ul) sends a signal at regular intervals to the battery to ensure that it is not running below a threshold voltage value of approximately 2.7V, and if it is, a beep will sound from the alarm sounder 14. It will be appreciated that the threshold voltage level can vary depending on the type of battery used, with higher voltage batteries having a higher threshold value and lower voltage batteries having a lower threshold value.

The microprocessor sends a signal which activates the alarm sounder 14 (LS) if the threshold temperature is detected.

In another embodiment, the temperature sensor may include a component supported underneath the board 8 by a thermal compound within the base 6. Alternatively, in another embodiment, the thermistor 13 may be approximately 1mm from the internal surface of the conductive base 6. - -

Either arrangement provides a heat transfer path through the tape 4, the metal base 6 at its platform 7 to the thermistor 13.

The base 6 is made of a thermally conductive material, in this case steel, which helps to transfer heat from the unit being monitored to the thermistor 13. The shell 2 is of plastics material and has a slot at either end so that the base 6 can clip onto it. The slots also assist sound emission from the buzzer 14 through the housing.

The shell 2 is removable so that the batteries can be replaced when necessary. The small hole 9 at the top of the plastics shell 2 allows the user to access the button 16 to test/silence the device. The button/switch 16 is used to test/silence the device. Once silenced, the device 1 will only sound again after a pre-set time if the pre-set temperature is still detected. The test button 16 is located slightly underneath the surface of the shell 2 so as the button is not pressed on accidentally.

Use of the Device 1 of Figs 1 to 6

The device 1 is able to detect the conditions for a fire before ignition happens, thereby acting as a very valuable fire -prevention device.

Referring again to Figs. 1 and 2, the device is attached using the double-sided thermal tape 4. One side of the tape 4 is on the raised platform 7 on the outer part of the thermally conductive metal base 6 and the other side of the thermal tape is used to attach the device 1 to the unit which is to be monitored, such as a phone charging adapter plug P. The connection via the thermal tape 4 between the conductive metal base 6 and the surface of the plug P creates a thermal path from the monitored unit to the resistor R12 and thermistor R13 through the thermal tape 4, the base 6 and its platform 7. Because of this thermal path, heat generated in the plug P is efficiently transferred to the device 1. This heat is sensed by the resistor R12 and the thermistor R13, and if the temperature sensed goes beyond a threshold temperature limit, the microprocessor Ul activates the alarm 14.

The sounding of the alarm 14 alerts users to the fact that the plug or device being monitored is overheating and is therefore in danger of igniting. This sounding of the alarm 14 alerts people in - - the surrounding area of this danger so that the danger can be acted upon before ignition occurs and a fire develops.

It is envisaged that the device 1 is particularly suited to the monitoring of charging devices for devices such as laptops, tablets and smartphones, and in particular to the monitoring of charging devices which are operated during the night. However, the device is not limited to this application and has multiple uses.

The device can be attached to plug tops, charger transformers, transformers, laptops, laptop chargers, desktop computers, desktop computer power leads, external hard drives, computer servers, e-cigarette chargers, dishwashers, washing machines, dryers, microwaves, sockets, socket pattress boxes, light pendants, light switches, light switch pattress boxes, spurs, fused spurs, immersion switches, immersions, time-clocks, emergency exit lighting, fire alarm control panel, extractor fans, radios, rc cars, isolator switches, cooker switches, cooker switch pattress boxes, lamps, fuse boards, electrical enclosures, electrical joint boxes, batteries, battery charging devices, battery boxes, televisions, multi-socket adapters, fridges, freezers, water coolers, irons, hairdryers, hair straighteners, hair curlers, electric blankets, games consoles, inverters, amplifiers, vacuum cleaners, electric heaters, doorbell sounder, doorbell transformer, power/charger leads, fryers, portable battery chargers, coffee machines, food processors, blenders, printers, scanners, projectors, electronic white boards, vending machines, digital TV boxes, DVD players, shredders, laminator, photocopiers or any other surface where temperature sensing is desired.

The device 1 can also be used as a marketing tool for companies in the same way that USB sticks are. A name or other branding indicia can be placed on the shell of the device and it can be given out during promotions.

Device 200 with Thermal Energy Harvesting In another embodiment, the battery is auto-powered by a heat harvesting device. Referring to Figs. 7 to 13, a device 200 comprises a housing 201 with a shell 202 and a thermally conductive base 203. The base 203 has a raised platform 204 with an adhesive pad 205 and the shell 202 has a low-profile shape having a part-circular outer profile in plan and a smaller dome 202(a) and a larger dome 202(b), as per the previously described embodiment. - -

Fig. 7 shows the device 200, with the housing 201, test button 215 and LED 216. As per the previous embodiment, the housing 201 comprises slots 221 and 222, but in this embodiment there are additionally slots 218 in the sides of both domes, again for venting. This helps to maintain thermal equilibrium within the device 200. In this case, the slots are particularly advantageous as they help circulation of air between the inside of the housing 201 and ambient air, this assists in maintaining the thermal gradient between the hot and cold sides of the energy harvester.

In this embodiment, the device comprises a double- sided circuit board 206 mounted within the housing 201. The circuit board 206 has a front face 206(a) and a rear face 206(b) and supports the following components:

207, microprocessor (Ul);

208, thermoelectric energy harvester (TEH) (rear face);

209, alarm sounder;

210, power management (PM) module;

211, rechargeable battery;

212, resistor (R12) forming part of a temperatures sensor;

213, aperture mounted thermistor (R13) also forming part of the overall temperature sensor (rear face);

214, wireless module (Bluetooth);

215, test/silence button

216, LED indicator

217, thermally- activated switch.

The device 200 is shown in perspective view in Fig. 7, and Fig. 8 shows the layout in logical terms, and Fig. 9 is an electrical schematic. As is clear from Fig. 8 the harvester 208 powers the power management module 210, which in turn powers the battery 211. The items in physical contact with the base 204 are the harvester 208, the thermistor 213 and also a thermally- activated switch 217.

As in the previous embodiment, the components R12 and R13 are a resistor and thermistor sensor working together to form the temperature sensor. This embodiment however has the - - additional features of a thermoelectric energy harvester (TEH) 208 for delivering power to recharge the battery 211.

In more detail, the rear face 206(b) of the circuit board 206 supports the thermoelectric energy harvester 208. As can be seen, the thermoelectric energy harvester 208 and the thermistor 213 are contained within the raised platform 204 of the base 203. The thermistor 213 and thermoelectric harvester 208 are alongside and parallel to each other, and are both in contact with the conductive base 203. This parallel arrangement means that the thermistor 213 and the energy harvester 208 are both independently exposed to the heat energy of the conductive base 203, and so each have separate thermal paths. Thus, the thermistor 213 can detect heat conducted by the base 203 and the energy harvester 208 can convert heat to electrical energy, simultaneously and independently of each other.

In this embodiment, the standoff of the platform 204 may be approximately 1 mm to 3 mm in order to accommodate the harvester 208. This arrangement means that the thermoelectric energy harvester 208 has a surface adjacent to the conductive base platform 204 and a surface adjacent to the circuit board 206. The lower surface is in contact with the base 203, for optimal thermal transfer. It is envisaged that in some embodiments there may be a thermally conductive paste between the harvester and the base, and likewise between the thermistor and the base.

The thermoelectric energy harvester 208 produces electricity from the temperature difference or thermal gradient of the two surfaces of the thermal path. It has two materials: an n-type and a p- type semiconductor (e.g. bismuth telluride, bismuth selenide), which produce electricity directly when their junctions are exposed to a temperature difference.

In principle, the n-type and p-type semiconductor materials are connected electrically in series, but thermally in parallel. A temperature gradient is maintained between the two parallel thermal (hot and cold) surfaces. As heat flows from the hot surface to the cold surface, the charge carriers (electrons and holes) within the semiconductor materials move along with the heat. This movement of charge carriers result in a net flow of current through an external circuit.

It is envisaged that the device 200 may utilise an off the shelf, commercially available, small scale thermoelectric energy harvester (TEH). - -

Typical commercially available thermoelectric energy harvesters can generate about 100 mV per °C of temperature difference between the hot and cold surfaces. The generated voltage is low (typically less than IV), and therefore an appropriate power management module is required to enhance the voltage level (to 3V - 5V) for charging a battery, such as that required by the invention.

In this embodiment, the power management module 210 is stand-alone and is solely responsible for power conditioning. It does not require the microcontroller 207 to achieve power conditioning. The thermoelectric energy harvester 208 has a surface in contact with the conductive base platform 204 and a surface adjacent to the circuit board 206. The platform 204 and the circuit board 206 are considered the warm and cold surfaces respectively.

It has been found by the inventors that under normal operating conditions the average temperature of the warm surface is in the range of 25 °C to 40 °C, and the average temperature of the cold surface 206 is in the range of 15 °C to 20 °C. Taking these average values, this means that the average temperature difference between the hot and cold surface is in the range of 5°C to 25°C. Furthermore, in cases where the device being monitored overheats, the warm surface 204 may reach temperatures of greater than 50°C. This will result in a higher temperature difference. Use of the Device 200

Advantageously, this temperature difference is used to power the circuit components of the device 200, including the battery 211. Taking the average values, the voltage generated by the thermoelectric energy harvester 208 application environment is in the range of 500 mV to 2.5 V. This is then converted to 3.3 V by the power management module 210 to charge the battery 211. The power management module 210 comprises a charge pump and DC-DC boost regulator circuits in order to convert variable low input voltage into stable regulated output voltage.

Referring to Fig. 8, this illustrates the flow of heat and the flow of energy from the thermoelectric harvester 208. As can be seen by the arrow, heat flows from the warm surface 204 to the thermistor 213 and to the energy harvester 208. The thermistor 213 detects when the temperature of the warm surface increases above a threshold temperature. As well as the thermistor 213, heat also flows in the direction of the energy harvester 208. As heat flows from the hot surface to the cold surface, the charge carriers (electrons and holes) within the semiconductor materials of the energy harvester 208 move along with the heat. This movement - - of charge carriers results in a net flow of current to the power management module 210 which steps up the voltage of the energy harvester 208. As can be seen, energy flows from the PM module 210 to the alarm 209, the thermistor 213, the wireless module 214 and the battery 211. As can also be seen in Fig. 8, there is a two-way flow of energy between the battery 211 and the power management module 210. This means that the device 200 may be powered by the battery 211 or by the energy harvester 208 when applicable. For example, in cases where there is little or no temperature difference between the warm surface 204 and cold surface 206, the power management210 will activate the battery power supply. In other cases when there is a sufficient temperature difference between the warm surface 204 and cold surface 206, the TEH 208 may, via the PM module 210, supply power to other components in the circuit as well as store excess energy into the battery 211.

The microcontroller 207 may also be configured to communicate with the wireless module 214. This may be to send an alert to a wireless paired device or to send a wireless signal to an external sounder in cases where the temperature of the monitored device rises above a threshold temperature.

The TEH 208 converts the heat flow from the warm surface to the cold surface due to the thermal gradient into electrical energy, which is delivered to the power management (PM) module 210. The PM module 210 converts the low voltage electrical energy delivered by the TEH 208 into higher voltage level and supplies the converted energy to the rechargeable battery 211 for storage in the form of electrical charge. The PM module 210 is connected to the rechargeable battery 211 through a two-way connection. It can deliver electricity to the battery through an electrical path, and simultaneously it can extract electricity from the battery through another electrical path.

The PM module 210 is also connected to the power supply rail that supplies electricity to the other modules (microcontroller, thermistor, wireless, radio) through two different electrical paths. One of these two electrical paths is controlled by a thermally activated switch (TAS) 217, and the other is controlled by the button/ push button 215 which is accessible to the user/ tester.

The PM module 210 controls the flow of energy to and from the battery 211. The output of the power management 210 is connected to the power supply rails either through the button 215 or - - the TAS 217 and the microcontroller 207 determines the flow of energy to the other components such as the thermistor 213, the alarm 209 and the wireless module 214. The microcontroller 207 is not directly connected to the battery, and it gets power from the battery or the TEG only through the PM module 210 when the button or the TAS 217 is closed.

Under normal operating conditions (such as factory settings, where the device has been manufactured, packaged and shipped to the consumer) both the power supply paths (the thermally activated switch 217 and the button 215) remain open. In this case the microcontroller, thermistor, wireless and alarm modules are electrically isolated from the PM module, and no electricity is supplied to them. However, the TEG, PM, and battery modules can still remain active and harvest thermal energy, if there is a thermal gradient of at least 2°C between the warm and cold surfaces. In all other cases, the entire unit will remain electrically inactive and none of the modules will consume any energy from the battery. The button 215 is accessible to the user/ tester and can be activated by the user to establish temporary electrical connection between the power management and the power supply rail. The button can be used to check the device and battery level by sounding the alarm. The button can also be used to initiate wireless connectivity (e.g. Bluetooth pairing) to a smartphone or other smart home hub, (such as Amazon Echo, Google Home etc.)

The thermally activated switch (TAS) 217 can be realized/ implemented by a thermostat (a bimetallic strip) and is in thermal contact with the warm surface 204. The TAS 217 connects the power management 210 to the power supply rail only when the warm surface reaches a substantially high temperature (45°C) which is a pre-set activation threshold.

When the warm surface temperature is higher than the activation threshold (45°C), the PM 210 is electrically connected to the power supply rail via the thermally activated switch 217 and the microcontroller 207 and the thermistor 213 are activated. The microcontroller 207 starts monitoring the warm surface temperature sensed by the thermistor. In case of an overheat detection (warm surface temperature 54°C or more) the microcontroller 207 activates the alarm and wireless modules to issue alert signals to the user. - -

In the unlikely event that both the TAS 217 and the button 215 are activated, the device will operate just as normal, since both of these switches (TAS and button) are essentially connected to the same supply voltage level at the PM side and the same supply rail on the other side. In all of the warm surface temperature ranges (Twarm < 45 °C, 45 °C < Twarm < 54°C, Twarm > 54°C) the TEG and power management module will continue to convert heat flow energy into electricity to recharge the battery.

The thermally activated switch (TAS) and the user accessible button provide means of electrical isolation between the PM and the power supply rail. This configuration ensures storage and preservation of electrical energy when the warm surface temperature is below the activation threshold, and supply electricity to the rails only when the temperature is above the activation threshold. Therefore, the incorporation of these isolation mechanisms will provide the device with longer shelf (storage) life and operational battery life.

Fig. 9 shows that the TEG generates low voltage electricity from thermal gradients, which is converted by the power management (PM) module into higher voltage level and is stored in the battery. The PM is connected to the supply rail through a thermally activated switch (TAS) and a user accessible button. The TAS connects the PM output to the supply rail only when the TAS is exposed to a pre-set activation threshold temperature via the warm surface. The user/ tester can activate the button to check the device/ battery level, sound the alarm or to initiate wireless connection to other smart devices (e.g. bluetooth pairing). Except for the above mentioned scenarios, the PM, battery and TEG remain electrically isolated from the power supply rail and the rest of the modules.

The microcontroller, thermistor, wireless and alarm modules can be supplied with the same power rail, and are connected to the same ground level.

Figs. 14 and 15 show that in use the temperature of the surfaces facing the base 204 are at a much higher level, and so the heat received via the base is efficiently channelled through the two desired thermal paths, for energy harvesting and for heat detection.

The device also has an LED 216 in order to provide a visible flashing output in addition to at the sound output. . .

Advantages

The device of the first embodiment has the major advantage that it is stand-alone, not requiring any connection to a power source and may be easily placed in position with no user skill required. It is completely non-invasive. The device of the second embodiment has the additional advantage that there will be no need to change the battery, as it takes advantage of the naturally- occurring temperature difference where it is used and good thermal conductivity of the device's base.

Also, the use of an energy harvester 208 in the device 200 has the following advantages:

• A compact, low weight, durable and efficient form of renewable energy is provided to the device

• The battery can be made much smaller. In embodiments where an energy harvester is not used, it is envisaged that a -200 mAh battery would be required. However, in cases where the harvester is used, this could be replaced by something as small as -10 mAh. This is because the battery is rechargeable and so less charge is required

• The harvester will provide the battery with an effectively unlimited source of energy, and offer a very long lifetime, approximately 10 years or more, before the need for battery or device replacement

• Instead of a lithium polymer battery, rechargeable alkaline batteries could be used, which would reduce the fire hazard significantly in cases of overheating

• The smaller size of the battery allows for more space within the housing 201 for other components, such as wireless communicators.

Furthermore, the device 200 is configured to detect the rise of temperature of an electronic device, it is particularly suited to the use of a thermoelectric energy harvester.

It is envisaged that in other embodiments:

an LED is provided to flash in addition to the sounder,

a wireless signal may be sent to an external sounder when a pre-set temperature is detected from the device in which the temperature sensing device is attached, additional sounders and sensors can be paired so that a network of sensors and sounders can be made. - -

The device may employ light and/or vibration output devices for alerting people who are hard of hearing or visually impaired.

It is also envisaged that the device may comprise a solar energy harvester, located on the external shell of the device 200.

It will be appreciated that the invention provides a simple and convenient way of achieving improved fire safety in homes and businesses. While most buildings will have fire alarms, it is envisaged that a device of the invention would react more quickly because it detects at a point of potential ignition the conditions for a fire in advance of it occurring.

The device of the invention has the following advantages:

simplicity of use, requires very little assembly and maintenance;

portable and can be moved onto different devices when needed;

low profile, does not obstruct from devices unnecessarily;

completely stand alone, does not require mains power;

direct heat transfer path and therefore efficient detection and alert.

The invention is not limited to the embodiments described but may be varied in construction and detail. The alarm device may be used with any device which may overheat, such as devices in an Internet of Things (IoT) network. It is also envisaged that the processor may be a very simple circuit, not a microprocessor, with a switch which provides a path from the battery to the output device if the temperature exceeds a certain threshold.

Claims

An alarm device comprising:

a housing (2) having a shell (3) and a thermally conductive base (6) and being arranged to be adhered to an object to provide a thermal path from an object, said housing containing;

a temperature sensor (12, 13);

a processor (11) linked with the temperature sensor (12, 13) and being configured to generate an alert if temperature above an alert threshold is detected, and

an output means for communicating an alert (14); and

a battery (B) providing power to the device.

An alarm device as claimed in any preceding claim, wherein the base (6) includes a resilient portion (4) for conformity with a curved object surface.

An alarm device as claimed in claim 2, wherein the resilient portion includes a resilient pad (4).

An alarm device as claimed in claim 3, wherein the adhesive pad (4) comprises double- sided adhesive tape.

An alarm device as claimed in any preceding claim, wherein the base (6) comprises a metal plate (7).

An alarm device as claimed in any preceding claim, wherein the base (6) includes a raised platform (7).

An alarm device as claimed in any preceding claim, wherein the base (6) comprises opposing hooks (20, 21).

An alarm device as claimed in claim 7, wherein the shell (2) comprises opposing slots (22, 23) for receiving the hooks of the base (6).

9. An alarm device as claimed in claim 8, wherein the base (6) and the shell (3) are flexible enough to allow snap-fitting of the hooks (20, 21) into the slots (22, 23).

An alarm device as claimed in any preceding claim, wherein the temperature sensor (12, 13) includes a component which is mounted in an aperture (26) of a substrate (8) supporting the temperature sensor.

11. An alarm device as claimed in any preceding claim, wherein the temperature sensor (12, 13) is mounted to be in contact with the base.

An alarm device as claimed in claims 10 or 11, wherein the aperture (26) is in a circuit board (8) within the housing (2), said circuit board supporting the temperature sensor (12, 13) and the processor (11).

An alarm device as claimed in any of claims 10 to 12, wherein the substrate aperture includes a thermally-conductive compound physically retaining the temperature sensor component in the housing, but allowing transfer of heat to the component.

An alarm device as claimed in any preceding claim, wherein the temperature sensor (12, 13) includes a transducer having a resistance which varies with temperature, and a reference transducer which is outside of a heat transfer path within the housing.

15. An alarm device as claimed in claim 14, wherein said reference transducer is mounted on a circuit board (8) on a side of said board opposed to the base (6).

An alarm device as claimed in any preceding claim, wherein the housing (2) includes at least one domed portion having a depth which is less than 50% of a maximum width dimension.

17. An alarm device as claimed in claim 16, wherein the depth is less than 40% of the width dimension and the area of the base is in the range of 400 mm 2" to 2000mm 2".

18. An alarm device as claimed in any preceding claim, wherein device depth is in the range of 7 mm to 12 mm, and its maximum lateral dimension is in the range of 40 mm to 55 mm.

19. An alarm device as claimed in any preceding claim, wherein the housing (2) has a configuration of overlapping domes (3(a), 3(b)).

20. An alarm device as claimed in any preceding claim, wherein the housing (2) has a top surface suitable for display of indicia.

21. An alarm device as claimed in any preceding claim, wherein the output means includes one or more selected from:

an audio sounder,

a light emitter such as an LED,

a vibratory device, and

a wireless communication interface.

22. An alarm device as claimed in any preceding claim, wherein the device includes a test and/or silence button and the processor has a corresponding test and/or silence function.

23. An alarm device as claimed in any preceding claim, wherein the test and/or silence button (16) is located to be accessed by a narrow tool via an aperture (9) in the housing.

24. An alarm device as claimed in any preceding claim, wherein the battery is rechargeable and the device comprises an energy harvester (208) and a power management module (210) for charging the battery.

25. An alarm device as claimed in claim 24, wherein the energy harvesting module is a thermal energy harvesting module (208) having a hot surface facing the base (203), and an opposed cold surface and is configured for generating an electrical charge arising from temperature difference between the hot and cold surfaces.

26. An alarm device as claimed in claim 25, wherein the thermal energy harvesting module (208) hot surface is mounted in contact with the thermally conductive base (203).

27. An alarm device as claimed in claim 26, wherein the thermal energy harvesting module (208) is housed between the circuit board (206) and the thermally conductive base (203).

28. An alarm device as claimed in any of claims 25 to 27, wherein the thermal energy harvesting module (208) is housed within a raised platform (204) of the thermally conductive base (203).

29. An alarm device as claimed in any of claims 25 to 28, wherein the thermal energy harvester (208) is in a thermal path which is separate from a thermal path to the temperature sensor (213).

30. An alarm device as claimed in claim 29, wherein the thermal energy harvester (208) is alongside the temperature sensor (213).

31. An alarm device as claimed in any of claims 24 to 30, wherein the power management module (210) is configured for stepping up the voltage received from the thermal harvesting module (208).

32. An alarm device as claimed in any preceding claim, wherein the device further comprises a thermally- activated switch (217) for activating components of the device only when an activation temperature of the base (203, 204) is detected.

33. An alarm device as claimed in claim 32, wherein the thermally- activated switch (217) is physically located in contact with the base (203, 204).

34. An alarm device as claimed in claims 32 or 33, wherein the device comprises a thermal energy harvester (208) linked with a rechargeable battery (211), and the thermally- activated switch (217) is located between a power management module (210) and the controller (207).

35. An alarm device as claimed in any preceding claim, wherein the housing (202) comprises at least four vents (221, 218) for temperature equilibrium with ambient.