SECURITY DEVICE

Abstract: There is described a security device for inhibiting the unauthorised tampering of an object having an electrically conducting portion. The security device comprises: a resilient electrical conductor (6) for providing an electrical connection with the electrically conducting portion; and circuit means for generating an alarm signal when the potential of the electrical conductor is not the same as a reference potential. The security device may be mounted in an expansion port of a computer or a peripheral device, and may further comprise movement sensing means.

Description: SECURITY DEVICE The present invention relates to a security device for inhibiting the unauthorised tampering of an obj ect having an electrically conducting portion . In particular, the present invention relates to a security device for inhibiting the unauthorised tampering of an item of computer hardware such as a personal computer . Theft of personal computer hardware is becoming an increasing problem in the modern world . In particular, theft of computer chips from inside a personal computer or other item of hardware is increasing . Attempts to solve this problem have centred on the provision of an alarm system which is triggered when the case of the computer hardware is opened. Sensors such as microswitches or photodetectors have been used to detect when the case is opened . However , the use of a microswitch can be defeated if the microswitch is held down manually while the case is opened. The use of photodetectors relies on the case being sealed against light which is not very practical and can be defeated by the case being opened in a dark environment . It is therefore an object of the present invention to provide an improved security device . According to the present invention there is provided a security device for inhibiting the unauthorized tampering of an object having an electrically conducting portion, the security device comprising : a resilient electrical conductor for providing an electrical connection with said electrically conducting portion; circuit means for generating an alarm signal when the potential of the electrical conductor is not the same as a reference potential. When the resilient electrical conductor is moved slightly, as will occur during unauthorised tampering of the object, the resilience in the conductor will cause the resistance of the contact between the conductor and the electrically conducting portion to change, resulting in an increase in the potential of the electrical conductor. Advantageously, the security device further comprises a reference conductor for providing an electrical connection with a common ground to provide said reference potential. Preferably, the security device further comprises a housing for the circuit means, the resilient electrical conductor being attached to the housing. Movement of the housing relative to the electrically conducting portion of the object therefore causes the alarm signal to be generated. In a preferred embodiment, the security device further comprises mounting means for mounting the housing in an expansion port of a computer or an associated peripheral device which is to be protected. The electrically conducting portion of the object is therefore the common ground of the case of the computer or associated peripheral device . When the case is opened, the electrical connection between the resilient electrical conductor and that part of the case which has been removed is broken, thereby causing the alarm signal to be generated. In one embodiment, tamper generation means are provided for generating a pulse if the potential of the electrical conductor is not the same as the reference potential. The tamper generation means may include timer means for generating a pulse after a timed interval if the potential of the electrical conductor remains not the same as the reference potential. The alarm signal is thereby repetitively triggered if the electrical connection between the resilient electrical conductor and the object remains broken e.g. if the case of the computer hardware remains open. Advantageously, the security device further comprises movement sensing means, such as vibration sensing means, for sensing movement of the housing. In this way, the security device can also detect and generate an alarm signal if, for example, the entire piece of computer hardware is moved without the case of the hardware being tampered with. Advantageously, the sensing device further comprises power enabling means for enabling the movement sensing means dependent on the nature of the power supply powering the security device. The provision of such a power enabling means allows the sensitivity of the security device to be automatically varied e.g. the protection afforded by the movement sensing means may be required when the computer hardware is switched off e.g. at night when no-one is around but not required during the day time when the hardware is switched on and people are around. Advantageously, the security device comprises an internal power supply for supplying a defined voltage and power supply connection means for connecting the security device to an external power supply for supplying a voltage greater than said defined voltage. In this way, the nature of the power supply powering the security device can be easily discriminated. Preferably, the movement sensing means is adapted to generate a signal having an amplitude dependent on the movement sensed. The circuit means further comprises movement generation means for generating a pulse if the amplitude of the signal from the movement sensing means exceeds a movement reference amplitude. These features reduce the risk of the alarm signal being generated if the movement sensing means is triggered by the computer hardware being accidentally knocked during the course of the day. However, the circuit means may be set to generate a pulse, and hence an alarm signal, if a large movement is sensed or if repetitive movement is sensed indicative of someone trying to move the piece of computer hardware. Advantageously, the circuit means comprises transmission means for transmitting the alarm signal to a remote receiver and encoding means for encoding the alarm signal to identify the security device from which the alarm signal is being sent. In this way, a plurality of security devices may be used to inhibit the unauthorised tampering of a plurality of objects such as an office housing many personal computers and associated computer peripherals. Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of a device according to the present invention; Figure 2 shows a block diagram of a circuit for use in the present invention; and Figure 3 shows a circuit diagram of the circuit of Figure 2. Figure 1 shows a security device for inhibiting the unauthorised tampering with the casing of a piece of computer hardware such as a personal computer or a computer peripheral. The device 1 comprises a housing 2 for containing the circuitry required to operate the device. A mounting plate 4 allows the device 1 to be mounted in an expansion port of the computer hardware which is being monitored. A resilient electrical conductor 6 is attached to the housing 2 of the device such that one end 6a of the conductor will come into contact with the inside metal casing of the computer hardware when the device 1 is mounted in position as defined by the mounting plate 4 in the expansion port. An aerial 8 is used to transmit an alarm signal from the device to a remote device . Also visible on the exterior of the device 1 are LEDs 10, 12. A block diagram and flow chart of a circuit for use with the security device is shown in Figure 2 and the detailed circuitry is shown in Figure 3. A power supply 16 is used to power the device and includes connections to the power supply to the computer hardware together with a rechargeable battery. When the computer hardware is switched on, 12 V is taken from the computer power supply and applied to the anode of D15. This is then taken through Dl and current limiting resistor R2 and fed to the other components in the circuit. The 12 V input is also fed through D2 and Rl to charge back-up battery Bl. If power to the computer hardware should fail or be turned off, Bl will supply the other circuitry through D3. D17 is a reverse polarity protection diode. The resilient electrical conductor 6 of Figure 1 forms part of a case tamper circuit 18. When the conductor 6 is in good electrical contact with the computer case, pin 4 of integrated circuit IC4 is held low. If the case of the computer hardware is moved or tampered with, the resistance of the electrical connection between conductor 6 and the computer case, and hence the potential of conductor 6 rises. The non-zero voltage at pin 4 of IC4 triggers pin 3 of IC4 to generate a pulse. IC4 comprises a comparator for comparing the voltage at pin 4 with a reference potential, ideally common ground, and a timer circuit. If the voltage at pin 4 of IC4 remains high, then a pulse will be generated periodically. The timing of the re-triggering is set by RIO, Rll, C4 and D7. In the example shown, a pulse will be generated every eight seconds if the voltage at pin 4 of IC4 remains high. The output of case tamper circuit 18 from pin 3 of IC4 is input to a flip-flop 20. (In the embodiment of Figure 3, an integrated circuit IC1 includes two flip-flops and so references to the pins for flip-flop 20 will refer to ICl/2 while references to the pins of the other flip-flop (flip-flop 28 of Figure 2) will refer to ICl/l) . When the flip-flop of ICl/2 is triggered, pin 13 switches high, turning on transistors TR1 and TR2 through R14 and R15 in the encoder circuit 22. Pin 13 remains high until C6 has charged to two thirds supply voltage and flip-flop 20 is re-set. The period for which pin 13 remains high allows sufficient time for a signal to be generated by encoder circuit 22. Obviously, if the case is not replaced, then pulses will be generated repetitively by the case tamper circuit 18 and hence pulses will be generated repetitively by the flip-flop 20. When TR2 in encoder circuit 22 is turned on, power is applied to IC3, which includes an oscillator circuit and to a three-position dip switch SW2. The dip switch SW2 is used to set a code identifying the security device so that an alarm signal encoded with the code can be transmitted from transmitter 24 to a remote receiver. If the remote receiver is monitoring many pieces of computer hardware, and hence security devices, the range of codes that can be set by dip switch SW2 may be insufficient to identify each security device, and hence piece of computer hardware, individually. Further switches e.g. SW3 may therefore be used to modulate the alarm signal to define address zones. The signal from the oscillator circuit in IC3 is fed through R21 to the transmitter module TXM1. Transmitter module TXM1 operates at 400-450 Mhz with either AM or FM modulation. Other frequencies can be catered for by substituting TXM1 with the appropriate module . In addition to the resilient conductor used to sense tampering of the case, the security device also includes a movement or vibration detector. The movement detector circuit 26 receives power from the power supply 16 through a relay RLA1. When power is available from the 12 V supply of the piece of computer hardware, the contacts of RLA1 are open and so the movement detector circuit 26, and associated circuitry flip-flop 28 and triggered latch 30, are disabled. When the power supply to the piece of computer hardware is switched off, the contacts of the relay close bringing R3 into the circuit. When movement is detected, VI momentarily closes and charges Cl through R3 , putting a voltage on pin 3 of ICl/1 of the flip-flop 28. When the voltage on pin 3 of ICl/1 exceeds two thirds of the supply to ICl/1, pin 1 of ICl/1 goes high, turning on TR1 of encoder circuit 22 through R14 and R15. A sufficiently high voltage may be generated at pin 3 of ICl/1 by a single movement detected by VI if this movement is sufficiently great. Alternatively, several smaller movements detected by VI will each generate a charge on Cl and accumulate to generate a sufficient voltage at pin 3 of ICl/1 to turn on pin 1 of ICl/1. However, isolated small movements will be insufficient to cause the flip-flop 28 to be triggered. Two seconds after the voltage on pin 1 of ICl/1 goes high, the voltage of C2 which has been charging through R5 exceeds two thirds supply voltage and causes the flip-flop to reset, discharging C2 through D5 in the process. The effect of TR2 in encoder circuit 22 being switched on has already been described with reference to operation of the case tamper circuit. When pin 1 of ICl/1 goes high, this also puts a high on pin 1 of IC2 of triggered latch 30 through D13 causing pin 4 of IC2 to latch and turn on LED2. This can be reset by closing switch SW1 or removing power to the circuit. R6 and CIO ensure that when power is first applied to the circuit, pins 8 and 9 of IC2 are held low disabling the latch circuit for five seconds. As described with respect to Figure 1, the security device includes two LEDs 10, 12. One LED 10, is LED2 of triggered latch 30 which indicates which security device has been moved sufficiently to cause an alarm signal to be generated. A second LED 12 is provided in the encoder circuit 22 and is switched on either if the movement of the entire piece of hardware is sufficiently great (movement detector 26) or if the case of the computer hardware has been tampered with (case tamper circuit 18) . The second LED 12 will also be switched on if the conductor 6 is not making a sufficiently good contact with the inside of the case during setting up of the security device.

Claims: CLAIMS : 1. A security device for inhibiting the unauthorized tampering of an object having an electrically conducting portion, the security device comprising: a resilient electrical conductor for providing an electrical connection with said electrically conducting portion; circuit means for generating an alarm signal when the potential of the electrical conductor is not the same as a reference potential. 2. A security device according to claim 1 further comprising a reference conductor for providing an electrical connection with a common ground to provide said reference potential. 3. A security device according to claims 1 or 2 further comprising a housing for the circuit means, said resilient electrical conductor being attached to the housing. 4. A security device according to claim 3 further comprising mounting means for mounting the housing to the object to be monitored. 5. A security device according to claim 3 further comprising mounting means for mounting the housing in an expansion port of a computer or an associated peripheral device. 6. A security device according to any one of the preceding claims wherein the circuit means further comprises tamper generation means for generating a pulse if the potential of the electrical conductor is not the same as the reference potential. 7. A security device according to claim 6 wherein the tamper generation means includes timer means for generating a pulse after a timed interval if the potential of the electrical conductor remains not the same as the reference potential. 8. A security device according to any one of the preceding claims further comprising movement sensing means for sensing movement of the housing. 9. A security device according to claim 8 further comprises power enabling means for enabling the movement sensing means dependent on the nature of the power supply powering the security device. 10. A security device according to claim 9 further comprising an internal power supply for supplying a defined voltage and power supply connection means for connecting the security device to an external power supply for supplying a voltage greater than said defined voltage. 11. A security device according to any one of claims 8 to 10 wherein the movement sensing means is adapted to generate a signal having an amplitude dependent on the movement sensed. 12. A security device according to claim 11 wherein the circuit means further comprises movement generation means for generating a pulse if the amplitude of the signal from the movement sensing means exceeds a movement reference amplitude. 13. A security device according to any one of the preceding claims wherein the circuit means comprises transmission means for transmitting the alarm signal to a remote receiver and encoding means for encoding the alarm signal to identify the security device from which the alarm signal is being sent. 14. A security device according to claim 13 as dependent on claim 6 wherein the tamper generation means is coupled to the encoding means whereby gneration of a pulse by the tamper generation means enables the encoding means. 15. A security device according to claims 13 or 14 as dependent on. claim 12 wherein the movement generation means is coupled to the encoding means whereby generation of a pulse by the movement generation means enables the encoding means. 16. A security device substantially as hereinbefore described with reference to any one of the accompanying drawings . 17. The combination of a security device according to any one of the preceding claims and a piece of computer hardware having an electrically conducting portion, the security device being mounted with the resilient electrical conductor in contact with the electrically conducting portion.

Inventors: HENDERSON PHILIP JAMES, HENDERSON, PHILIP, JAMES
Applicants: DASHCROWN LIMITED, HENDERSON PHILIP JAMES, HENDERSON, PHILIP, JAMES
Application year: 1997
Main classification: G08B13
IPC codes: G08B13