TECHNICAL FIELD

[0001] The present invention relates to an enclosure for an alarm node, comprising a tamper detecting device.

PRIOR ART

[0002] A prior art tamper detecting device configured to detect separation of an enclosure from a wall bracket comprises a mechanical switch that is maintained in a closed position when the enclosure is attached to the wall bracket. When the enclosure is moved away from the wall bracket the me chanical switch is opened and an alarm event is triggered. An example of an alarm system using a tamper detector is disclosed in WO 2007/021729 A2.

SUMMARY OF THE INVENTION

[0003] In accordance with a first aspect there is provided an enclosure for an alarm node, comprising a tamper detecting device configured to detect relative movement between a metal element and an inductive detector, wherein the inductive detector comprises an oscillator with a frequency set ting inductor and wherein a frequency detecting unit is operatively connected to the inductive detector and configured to trigger an alarm event when a change of the oscillator frequency larger than a predetermined value has been detected.

[0004] A device according to embodiments of the invention may be less dependent on narrow tolerances in dimensions between the enclosure and components within the enclosure and an element mounted on a mounting surface. There will be less challenges in mechanical design and no internal stresses due to compression of a mechanical switch. There will also be sub stantial cost benefits, such as around 30 per cent lower costs, as compared to using a traditional mechanical switch. [0005] Various embodiments of the invention will also be able to detect tampering in situations where the enclosure is mounted on a wall bracket, and the wall bracket is removed from a mounting surface together with the enclosure. This could happen if the wall bracket is not sufficiently fastened to the mounting surface.

[0006] Embodiments of the invention can be used in a wireless communi cations system comprising a plurality of wireless nodes including a first gate way, one or more wireless alarm peripherals and, in some installations, one or more further gateways. The wireless communications system can form part of a home alarm system installation that comprises at least one wireless alarm detector and at least one gateway. The wireless alarm detector will sig nal alarm events to the gateway. If any of the devices or nodes fail - some action is taken, such as signaling to the gateway and notifying the home owner or triggering a tamper alarm. Signaling of alarm events and tamper alarms can comprise generation of an alarm signal in premises where the alarm system installation is installed and/or forwarding an alarm signal to a remote central monitoring station where further steps for managing the situa tion can be taken.

[0007] A home alarm system installation in general can be any type of wireless systems comprising a plurality peripheral wireless nodes, such as an intruder alarm, and a central unit. Specifically, it can be a security system having a plurality of nodes including wireless detectors, sensitive to the dis placement of windows and doors, and to presence or passage of persons and objects, and sensitive to smoke or water leakage, the detectors com municating with a central unit such as a gateway using wireless communica tion. Security and alarm systems may comprise a control panel. The system may comprise a gateway that is connected to a remote central monitoring station, either by a telephone line or by a wireless telecommunications sys tem such as GSM or other radio frequency systems. The connection can also be through the internet. The control panel can be provided with an input de vice or be activated and controlled by a control device such as a keypad which can be a wireless remote device. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Non-limiting embodiments of the invention will now be described with reference to the figures in which:

Fig. 1 is a schematic view of an installation of a home alarm system instal lation,

Fig. 2 is a schematic diagram showing a typical home alarm system instal lation including two communication units,

Fig. 3 is a schematic diagram showing a first embodiment of an enclosure with a tamper detecting device,

Fig. 4 is a schematic diagram showing a second embodiment of an enclo sure with a tamper detecting device,

Fig. 5 is a schematic perspective view of an enclosure with a tamper de tecting device, and

Fig. 6 is a schematic diagram showing an embodiment of an oscillator that can be used in the tamper detecting device of any of the enclosures shown in Fig. 3 to Fig. 5.

DETAILED DESCRIPTION

[0009] Fig. 1 shows a home alarm system installation in a building 10. The home alarm system installation comprises a plurality of nodes including wire less peripheral devices, a first gateway 12 and a second gateway 12’. The second gateway 12’ is mains powered. One wireless peripheral node is a first infrared detector 14 mounted in the corner of a first room 13 close to the ceil ing. The first infrared detector 14 has a sensing area that covers the first gateway 12 also disposed in the first room. A camera can be included in the infrared detector 14 or it may form a separate wireless peripheral device. During alarm events, the camera transmits video signals or other images to the gateway 12, 12’. The infrared detector 14 operates in a conventional manner to detect presence and movements of objects emitting infrared radia tion.

[0010] Another node is a first perimeter alarm detector 16 is mounted at a window 17 in the same room. The perimeter alarm detector can operate in a conventional manner to detect when a door or a window is opened. In vari ous installations the perimeter alarm detector comprises a magnetic sensor that will detect when a magnet attached to the door or window is moved.

[0011] A second gateway 12’ is arranged in a second room 15 separated from the first room 13 where the first gateway 12 is arranged. A second infra red detector 14’ is mounted in the same room as the second gateway 12’ to cover the second gateway within its sensing area, and a second perimeter alarm detector 16’ is mounted at a second window 17’ in the same room. A keypad 19 is mounted close to a front door 20 of the building 10. The keypad 19 is used by a user of the alarm system to arm and to disarm the alarm sys tem. The keypad 19 also is a wireless peripheral node. The front door 20 is covered by a third perimeter alarm detector 21. Another type of wireless pe ripheral device is a smoke detector 23 mounted in the ceiling of the building. In various installations a plurality of smoke detectors 23 is arranged through out the building 10 to ensure that fire can be detected at an early stage.

[0012] Depending on different circumstances the first gateway 12 and the second gateway 12’ are connected to a remote central monitoring station 22 either through a wired connection 24 or through a wireless connection such as GSM or a similar digital cellular network 34. The connection to the remote central monitoring station 22 can also be through the internet 26. In the in stallation shown in Fig. 1 , internet connection is provided through a wireless router 32 that is connected to internet by fiber, cable or Digital Subscriber Line, such as ADSL, or in any similar way. In the installation shown in Fig. 1 the second gateway 12’ is connected by wire 33 to the wireless router 32.

The wired connection 24 can be part of a public switched telephone network 25. In various installations the remote central monitoring station 22 comprises an interface module 27, a database 28 and a web server 29. The database 28 stores installation and application data relating to the installation including all wireless network nodes and alarm settings.

[0013] By placing gateways strategically within a building, it is possible to ensure that all peripheral nodes have an adequate RF link with at least one gateway. As long as each gateway can communicate directly with at least one other gateway and directly or indirectly with all of the other gateways, the installation will function properly. To achieve full redundancy the installation should include enough gateways for every peripheral node to be able to com municate with at least two gateways.

[0014] An installation such as the alarm system shown in Fig. 1 holds a large amount of dynamic state information, such as arm state, alarm status, peripheral battery status, etc. in a total system state information dataset. Sim ilar information is stored also in other types of home wireless systems. Each gateway or controller continuously receives inputs from different authenti cated sources such as peripheral nodes, a remote central monitoring station (RCMS), adjacent systems, etc. that affects a distributed state of the applica tion or system. In various installations, a second gateway can utilize the RF communication link of another gateway for tunneling messages to an RCMS. For example, if the second gateway up-link to RCMS is very slow or unreach able, or has a higher cost, another gateway up-link can be utilized.

[0015] The alarm system can be armed in different ways and into different alarm system states, such as“Disarmed”,“Armed Home” and“Armed Away”. If the system is set to "Disarmed" it will not alarm to perimeter or interior de tectors. Still, fire detectors, other gas detectors, flooding events, power break down events and similar detectors normally will be armed also in the“Dis- armed” state. If the alarm system is set to a first armed state referred to as "Armed Home" the alarm system will generate an alarm at the occurrence of a breach of a first group of selected detectors such as perimeter detectors and selected interior detectors, but not to a breach of interior detectors in general. If the system is set to a second armed state referred to as "Armed Away", it will alarm to a breach of the perimeter or interior detectors and nor mally to all types of detectors. [0016] A basic installation is shown in Fig. 2. This installation relates to a home alarm system comprising a first gateway 12, a second gateway 12’ and at least one wireless peripheral device, such as an infrared detector 14. The first gateway 12, the second gateway 12’ and the infrared detector 14 all communicate using radio communication. At least one gateway is repeatedly communicating with the remote central monitoring station 22 as disclosed above.

[0017] The first and the second gateways 12, 12’ comprise first communi cation units 36 and second communication units 38. First communication units 36 is used for communicating with the remote central monitoring station 22 either through a wired connection 24 or through a wireless connection such as GSM or a similar digital cellular network. The connection to the re mote central monitoring station 22 can also be through a wired connection, such as a public switched telephone network or the internet. Video and other images will be transmitted to the remote central monitoring station 22.

[0018] The second communication units 38 is mainly used for communica tion within the installation between gateways and between gateways and pe ripheral nodes. Each gateway is controlled by a control unit 40 and com prises a power unit 42, normally a battery. At least one gateway can be pro vided with a detector 44 continuously monitoring radio communication re ceived in the gateway. When detector 44 detects intentional or unintentional radio disturbance measures in the radio communication system an alert sig nal is transferred to control unit 40. An alarm signal then can be generated in the gateway and forwarded to the remote central monitoring station 22 in an appropriate way.

[0019] A basic embodiment of an enclosure 60 comprising a tamper de tecting device 46 is shown in Fig. 3. The tamper detecting device 46 com prises an inductive detector 48 configured to interact with a metal element 50. The inductive detector 48 comprises an oscillator 52 with a frequency set ting inductor 54. The inductive detector 48 is operatively connected to a fre quency detecting unit 56. The frequency detecting unit 56 can be implemented in a microcontroller. In various embodiments, the frequency de tecting unit 56 comprises a separate frequency counting device 57.

[0020] When the wireless peripheral node is mounted on a mounting sur face such as a wall or ceiling, the frequency setting inductor 54 is positioned in the vicinity of the metal element 50. In this position, the metal element 50 will interact with the frequency setting inductor 54 and bias its inductive prop erties. As a result, the frequency of the oscillator will change, should the metal element 50 and the frequency setting inductor 54 be moved in relation to each other. A frequency change over a threshold value will be detected as a tamper attempt, and an alarm will be triggered by sending an alarm signal to a gateway 12; 12’.

[0021] Surface mounted nodes, such as gateways, detectors and other pe ripheral units comprise the enclosure 60 with the tamper detecting device 46 configured to detect separation of the enclosure 60 from a mounting surface 64. In various embodiments, a wall bracket 62 is attached to the mounting surface 64 and the enclosure 60 is attached to the wall bracket 62. The metal element 50 is associated with the wall bracket 62 and the inductive detector 48 is associated with the enclosure 60. As shown in Fig. 3, the metal element 50 is provided in the wall bracket 62 and the inductive detector 48 is ar ranged in the enclosure 60. In various embodiments, the metal element 50 is a screw 51 used to attach the wall bracket 62 to the mounting surface 64, such as a wall or the ceiling.

[0022] In the embodiment shown in Fig. 4, the metal element 50 is pro vided in a mounting support 63 that is independently attached to the mount ing surface 64, such as a wall or ceiling. The enclosure 60 can be attached to the wall bracket 62. One or a plurality of attachment screws 53 are used to attach the wall bracket 62 to the mounting surface 64. If someone pulls the enclosure in accordance with Fig. 3 or Fig. 4 of the mounting surface, the in ductive detector 48 will move relative the metal element 50; 51 , giving rise to a reliable tamper protection of the enclosure.

[0023] In various embodiments, electronic circuits of the tamper detecting device 46 are mounted or arranged on a printed circuit board 66, PCB, as shown in Fig. 5. In the embodiment shown in Fig. 5, the PCB 66 is a multi layer board and the frequency setting inductor 54 is a metal trace winding 68 on the PCB 66. In various embodiments, the metal trace winding 68 extends over at least two layers of the PCB 66. The oscillator 52 is also arranged on the PCB 66 as well as the frequency detecting unit 56. A bottom layer 72 of the PCB 66 visible in Fig. 5 is facing the metal element 50, and the metal trace winding 68 in the top layer will be in the vicinity of a metal element 50 when the enclosure 60 with the PCB 66 is properly mounted on the wall 64.

[0024] A shielding element 70 is formed on a top layer 58 of the PCB 66. The shielding element 70 can be one metal layer on the multi-layer PCB and will decrease effects on the frequency setting inductor 54 of metal objects present or moving outside the enclosure 60 close to the top layer 58. In an example, the frequency setting inductor 54 has a diameter of 7 mm. It will be capable of detecting metal elements at a distance of several millimeters, such as at least 5-10 mm. The metal element preferable is at least 5 mm in diameter. A plurality of other components 74 is also mounted on the top layer 58 of the PCB 66.

[0025] The frequency of the oscillator 52 may vary due temperature sensi tivity of components used in the oscillator 52. A changing oscillating fre quency could be interpreted as a tamper attempt and cause a false alarm. This situation can be avoided by using a reference oscillator 52’ and an asso- ciated reference frequency setting inductor 54’ and by detecting a frequency difference between the oscillators 52, 52’. Preferably, the two oscillators 52, 52’ and the two associated frequency setting inductors 54, 54’ are identical or have identical properties, at least with regard to impact by temperature varia tions.

[0026] If the oscillating frequency of the oscillators 52; 52’ changes due to temperature variations both oscillators 52, 52’ be affected the same way and there will be no frequency difference or only a small difference below a threshold value. However, should the inductive detector 48 be moved in rela tion to the metal element 50 the frequency of the oscillator 52 will change while the frequency of the reference oscillator 52’ will remain substantially the same. Thus, there will be a detectable frequency difference between the two oscillators and an alarm will be triggered.

[0027] Fig. 6 shows one embodiment of the oscillator 52 comprising a plu rality of components. The frequency setting inductor 54 is connected be tween power V and the collector of a transistor Q1. The transistor Q1 is fed from power V by first resistor R1 and second resistor R2 in series with the first resistor R1 , the base of transistor Q1 being connected between the first resistor R1 and the second resistor R2. The first resistor R1 is connected to power V and the second resistor R2 is connected to ground GND. The emit ter of transistor Q1 is connected to ground GND through a third resistor R3. A first capacitor C1 and a second capacitor C2 in series are connected in paral lel with the frequency setting inductor 54. The emitter of the transistor Q1 is connected to a connection point between first capacitor C1 and second ca pacitor C2. A third capacitor C3 is connected in parallel with second resistor R2. The frequency of the oscillator 52 will vary as the square root of the in ductance of the frequency setting inductor 54. An oscillating signal is output from the collector of the transistor Q1 and fed to the frequency detecting unit 56. In one example, the components are:

R1 : 100 kOhm

R2: 100 kOhm

R3: 1 kOhm

C1 : 22 nF

C2: 2.2 nF

C3: 1 nF

Q1 : BC847C

[0028] While certain illustrative embodiments of the invention have been described in particularity, it will be understood that various modifications will be readily apparent to those skilled in the art without departing from the scope and spirit of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description set forth herein but rather that the claims be construed as encompassing all equivalents of the present invention which are apparent to those skilled in the art to which the invention pertains.