GB2338812A

GB2338812A - Alarm system with anti-tamper devices

Info

Publication number: GB2338812A
Application number: GB9813695A
Authority: GB
Inventors: Andrew Rust
Original assignee: Texecom Ltd
Current assignee: Texecom Ltd
Priority date: 1998-06-26
Filing date: 1998-06-26
Publication date: 1999-12-29
Anticipated expiration: 2018-06-26
Also published as: GB9813695D0; GB2338812B

Abstract

An alarm system (10) comprises at least one sensor (11) which is connected to a central control panel (12). The sensor (11) acts to detect the presence of an intruder and sends an alarm signal to the control panel (12). The control panel (12) in turn upon receipt of the alarm signal sends a signal to an alarm indicator (13) which can include both a visual alarm in the form of a flashing or stroboscopic light and/or an audible alarm in the form of a piezo electric buzzer. Each of the sensor (11), control panel (12) and alarm indicator (13) have an anti-tamper device associated with them which causes the production of an alarm signal if an intruder attempts to gain access to the internal parts of these devices to disable or interfere with operation of the alarm system. In the improved system of the invention, it is possible for an engineer to enter a code into the control panel (12). In response, a predetermined number of signals over a predetermined period of time are sent to the alarm indicator (13) to deactivate the anti-tamper device. This means that a bone fide engineer can deactivate the anti-tamper devices so that routine service and maintenance work can be carried out safely.

Description

2338812 AN IMPROVED AILARM SYSTEM This invention relates to an improved

alarm system for domestic or commercial premises.

Conventional alarm systems for domestic or commercial premises usually comprise a control panel, a number of detectors linked to the panel and one or more alarm indicators, for example an audible alarm device andlor visual alarm device. The audible alarm device usually comprises a bell or piezo electric buzzer and the visual alarm device usually comprises a flashing or stroboscopic light. Furthermore, it is common for an alarm indicator to comprise a so called "bell box" which usually incorporates both visual and audible alarm devices.

Usually the individual parts of an alarm system are provided with antitamper devices which are operable to send a signal to the control panel when a part of the system is tampered with in an attempt to gain access to the internal workings of the part in an attempt to disable the alarm system. The anti-tamper device usually comprises a switch which is opened if any attempt is made to gain entry to the internal workings and the opening of the switch is detected by the control panel which is operable automatically to cause activation of the alarm indicator.

For maintenance or repair of the alarm system, it is necessary for an engineer to be able to gain access to the internal workings of the various parts of -2the alarm system without causing activation of the alarm indicator. It has been proposed to adapt the control panel to allow an engineer to enter a security code into the control panel which would cause the control panel no longer to cause activation of the alarm indicator upon detection of tampering with any part of the alarm system. However, whilst this operation would successfully prevent activation of the alarm indicator upon detection of tampering with any part of the alarm system, unfortunately with an alarm indicator, tampering with this indicator causes activation of the indicator completely independently of the control panel resulting in the activation of the alarm device. Therefore entry of a code at the control panel in this system will prevent the control panel from causing activation of the alarm indicator upon tampering but will not prevent the alarm indicator automatically activating upon tampering with the indicator.

It is an object of the present invention to provide an improved alarm system in which the activation of the alarm indicator, upon detection of tampering therewith, whether this be under the control of the control panel or independent thereof, can be prevented allowing maintenance and repair operations to be carried out on the internal working of the alarm indicator safely.

Thus and in accordance with the present invention therefore there is provided an improved alarm system comprising a control device, at least one detector and at least one alarm indicator linked to the control device, said at least one alarm indicator having an anti-tamper device associated therewith operable to -3cause the production of an audible and/or visual alarm by said alarm indicator when tampered with, wherein said control device is operable, after entry of a security code, to send a predetermined number of alarm indicator activation signals to said alarm indicator over a predetermined time period, said signals being operable to prevent said alarm indicator being activated upon detection of tampering with said indicator by said anti-tamper device.

With this arrangement it is possible for an alarm indicator to be rendered unresponsive to tampering.

It is envisaged that the security code will only be made available to bona fide service engineers whereby the alarm indicator can only be rendered unresponsive to tampering by such persons.

Preferably the alarm indicator includes an audible alarm device such as a bell or piezo electric buzzer and may also include a visual alarm device such as a stroboscopic light or flashing light.

Preferably the alarm indicator includes an indicator device which is actuated upon receipt of the predetermined number of signals to indicate that the indicator can be tampered with without causing activation of the alarm indicator.

Preferably said alarm indicator is adapted to automatically cause said alarm -4indicator to revert to a condition whereby tampering with said alarm indicator causes the alarm indicator to be activated after a maximum time period of approximately 20 minutes from receipt of said predetermined signals. Most preferably, the alarm indicator will revert to this condition approximately 2 minutes after the last tampering with the alarm indicator.

The invention will now be described further by way of example only and with reference to the accompanying drawings in which:

Fig. 1 shows a schematic representation of a conventional alarm system; Fig. 2 shows a typical signal sent by a control panel to the alarm indicator in the system of Fig. 1 which causes activation of the indicator in the event of tampering with any part of the alarm system; and Fig. 3 shows a signal which can be sent in the system of present invention, after entry of a security code, by the control panel and which is operable to prevent activation of the alarm indicator when it is tampered with.

Referring now to the drawings, there is shown in Fig. 1 a schematic diagram of a conventional security alarm system for protection of domestic or commercial premises. The system 10 comprises at least one sensor 11 connected to a central control panel 12, the sensor acting to detect the presence of an intruder and send -5an alarm signal to the control panel 12. An alarm indicator 13 is also connected to the control panel 12 which is operable to produce an alarm under the control of the control panel 12 upon detection of an alarm signal produced by the sensor 11. The alarm indicator usually includes a visual alarm indicator such as a flashing or stroboscopic light and an audible alarm indicator such a piezo electric buzzer which respectively produces both a visual and an audible alarm when an alarm signal is detected by the control panel 12. This type of alarm indicator 13 is commonly referred to as "a bell box".

In use an intruder is detected by the sensor 11 which causes the production of an alarm signal which is sent to the control panel 12. The control panel 12, upon receipt of an alarm signal from the sensor 11, sends a signal to the bell box 13 which produces both an audible alarm and a visual alarm. This audible and visual alarm is intended to notify persons nearby of the intruders presence and to deter the intruder from carrying on his activities. In itself, the presence of an alarm system on premises can be a deterrent to intruders.

In the system mentioned above, each sensor 11, the control panel 12 and the bell box 13 have an anti-tamper device associated with them which is arranged to cause an alarm signal to be sent to the control panel 12 if any of the parts of the system are tampered with in an attempt to gain to access to the interior of any of the parts to disable or interfere with operation of the alarm system. This alarm signal is detected by the control panel 12 which in turn activates the bell box 13 -6to create an audible and visual alarm in the manner mentioned above.

It is necessary with alarm systems for routine maintenance and service operations to be carried out by an engineer. Obviously whilst these service or maintenance operations are being carried out it will be necessary for the engineer to gain access to the internal workings of various parts of the system. Of course, because, as mentioned above, all of the parts of the system are provided with antitamper devices, in order to prevent the bell box providing an alarm when any part of the system is tampered with by a bona fide engineer, the control panel 12 of these conventional systems is adapted whereby if a particular code (the "engineer code") is entered into the control panel 12, whilst an alarm signal will still be sent to the control panel 12 by the anti-tamper devices, the control panel 12 will not activate the bell box 13 to produce a visible and audible alarm. This means that the engineer can carry out routine maintenance and servicing of the alarm system without the bell box 13 producing an alarm.

However, a problem arises in this conventional system insofar as whilst the entry of the engineer code into the control panel 12 results in the bell box 13 not being activated by the control panel 12 upon detection of tampering with any part of the system, this will not usually prevent the bell box 13 from producing an alarm if the bell box 13 is itself tampered with whilst carrying out maintenance or servicing. This arises because the bell box 13 is, in conventional systems, adapted to produce an alarm immediately when tampered with and it will produce this -7alarm whether or not a signal to do so is received from the control panel 12. This is referred to as "self activation" of the bell box 13 and is completely independent of the control panel 12. Therefore entry of the engineer code into the control panel 12 will not prevent this "self activation" of the bell box 13.

Therefore it will be appreciated that with these conventional systems it is not possible for an engineer to carry out routine maintenance or servicing on the bell box without the bell box producing an alarm. This is clearly not in the interests of the engineer since firstly if he is working in close proximity to the bell box 13 when the alarm is sounded, damage to his hearing can be the result as the audible alarm can exceed 110 decibels. Furthermore, the engineer may, if the alarm is sounded, be assumed to be an intruder.

The present invention is directed to this problem and seeks to provide a means whereby self activation of the bell box 13 upon tampering therewith can be prevented in order that an engineer can carry out routine maintenance and servicing on the bell box 13 in safety.

The present invention solves this problem by providing a means whereby the self activation of the bell box 13 can be prevented by appropriate engineer interaction with the control panel 12 after entry of the engineer code. The invention involves no modification to the general layout of the conventional alarm system shown in Fig. 1, but does involve a modification to the bell box 12 in order -8that these can operate in a manner which will now be described with reference to Figs. 2 and 3 of the drawings.

Fig. 2 shows a representation of the voltage signal which normally passes between the control panel 12 and the bell box 13 when tampering has been detected and the bell box is to be activated. The drop in voltage at time T1 to zero volts causes the bell box to sound both audible and visual alarms. Tampering with the bell box causes the voltage on a tamper connection between the control panel 12 and the bell box 13 to become open circuit very quickly. The control panel 12 detects this change in voltage and causes the activation of the bell box 13 by sending a signal of the type shown in Fig. 2 as described above. As discussed above if the bell box 13 is tampered with even when control panel 12 has been instructed, by entry of the engineer code, to not cause activation of the bell box 13 upon detecting tampering with the bell box 13, self activation will still occur.

In the system of the invention, the control panel is modified such that, after entry of the engineer code, it is possible by interaction with the control panel 12 to cause a signal of the type shown in Fig. 3 to be sent from the control panel to the bell box 13. The bell box 13 is adapted such that upon detection of this type of signal, self activation of the bell box on tampering is prevented. The signal consists of a predetermined number of voltage drops on the connection between the control panel 12 and the bell box 13 within a predetermined time. Thus in the example shown, if 3 voltage drops are detected within a time T2 then the bell box 13 will render itself incapable of self activation. Thus it can be seen that each voltage drop in the signal Fig. 3 is essentially the same as the voltage drop in the signal shown in Fig. 2 which causes activation of the bell box 13 upon tampering therewith. Thus the signal will render the bell box 13 incapable of self activation, and so is referred to as the "hold off" signal and is essentially a predetermined number of alarm signals in a predetermined time.

Whilst in the examples shown in Fig. 3, three voltage drops are necessary to cause the bell box to become incapable of self activation, it will be appreciated that the signal can be arranged such that any number of voltage drops, as desired or as appropriate, can be sufficient to allow this to happen.

Conveniently the sending of the signal of the form shown in Fig. 3 is achieved by entry of an appropriate code into the control panel. The entry of the code into the control panel causes the panel to send the signal to the bell box. In this case the entry of the appropriate code will only send a signal of the type shown in Fig. 3 after an appropriate engineer code has been entered. As a still further alternative, a series of voltage drops of the type shown in Fig. 3 can be applied to the bell box 13 by a simple manual connection of the connection between the control panel and the bell box 13 to either positive or negative power supply terminals within the control panel 12. If this manual connection is made in an appropriate manner a signal of the type shown in Fig. 3 can be provided on the connection to prevent self activation of the bell box 13.

1 It is envisaged that once a signal of the type shown in Fig. 3 has been sent to the bell box 13 and the bell box 13 is incapable of self activation, that the bell box 13 will be adapted such that after a maximum period of 20 minutes, the bell box 13 will cause itself to revert to a state in which it is capable of self activation. In a particularly preferred embodiment, the alarm indicator will revert to this condition approximately 2 minutes after the last tampering with the alarm indicator. This will prevent an engineer from inadvertently leaving the alarm system in a state whereby the bell box is incapable of self activation thereby allowing tampering with the alarm system.

Thus it will be appreciated that the arrangement of the present invention provides an alarm system in which the bell box can be routinely serviced and maintained without the production of an audible or visual alarm by the bell box when it is tampered with. This in particular has a number of noise pollution benefits and also prevents an engineer from having to work in close proximity to a very loud alarm which can cause damage to hearing if this work is carried out on a protracted or regular basis.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

11

Claims

1 An improved alarm system comprising a control device, at least one detector and at least one alarm indicator linked to the control device, said at least one alarm indicator having an anti-tamper device associated therewith operable to cause the production of an audible and/or visual alarm by said alarm indicator when tampered with, wherein said control device is operable after entry of a security code to send a predetermined number of alarm indicator activation signals to said alarm indicator over a predetermined time period to signals being operable to prevent said alarm indicator being activated upon detection of tampering with said indicator by said anti-tamper device.

2. A system according to claim 1, wherein the alarm indicator includes an audible alarm device, 3. A system according to claim 2, wherein the audible alarm devi,e compiises a bell.

4. A system according to claim 2, wherein the audible alarm device comprises a piezo-electric buzzer. A system according to any one of claims 1 to 4, wherein the alarm indicator includes a visual alarm device. A system according to claim 5, wherein the visual alarm device comprises a stroboscopic light. A system according to claim 5, wherein the visual alarm device 6.

12comprises a flashing light.

8. A system according to any one of claims 1 to 7, wherein the alarm indicator includes an indicator device which is actuated upon receipt of the predetermined number of signals to indicate that the indicator can be tampered with without causing activation of the alarm indicator.

9. A system according to any one of claims 1 to 8, wherein the alarm indicator is adapted to automatically cause said alarm indicator to revert to a condition whereby tampering with said alarm indicator causes the alarm indicator to be activated after a maximum time period of approximately 20 minutes from receipt of said predetermined signals.

10. A system according to claim 9, wherein the alarm indicator reverts to a said condition approximately 2 minutes after the last tampering with the alarm indicator.

11. An improved alarm system substantially as hereinbefore described with reference to Figures 2 and 3 of the drawings.