GB2156120A - Alarm system - Google Patents

Abstract

Sensing of an alarm condition at a local monitoring station 1 causes a radio frequency transmitter 6 to transmit an alarm signal with an associated identification component to a remote command station 11 which produces an output indicating an alarm condition and the associated identification component to audio and/or visual alarm display means 14, 15 and 16. <IMAGE>

Description

SPECIFICATION Alarm system The present invention relates to alarm systems in general including, for example, burglar alarms and fire alarms.

The effectiveness of an alarm system is dependent very much on triggering of the alarm being detected by someone in a position to take appropriate action. For this reason many properties have burglar alarms which are connected to the telephone system and arranged to telephone the local police station, central station or predetermined number when they are triggered.

Such known alarm systems can however be readily inactivated by cutting of the telephone line. Moreover, the information that can be given over the telephone with such a system is extremely limited and is generally no more than the address of the property which is given by a prerecorded message. Should the listener have difficulty in understanding the message, e.g. because of a poor line, then many minutes can be wasted waiting for the message to repeat and attempting to understand the message. Furthermore, it is not possible to effect any exchange of information with the property at which the alarm is located, for example, to check for a false alarm.

It is an object of the present invention to avoid or minimize one or more of the above disadvantages.

According to the present invention there is provided an alarm system comprising a local monitoring station and a remote command station, wherein the local monitoring station comprises at least one sensor adapted to sense an alarm condition, local control means adapted to monitor the output of said at least one sensor and a radio frequency transmitter adapted to transmit an alarm signal with an associated identification component andto be activated by said local control means when an alarm condition is sensed by at least one of said sensors, and the remote command station comprises a radio frequency receiver adapted to receive an alarm signal transmitted by the radio frequency transmitter, signal processing means adapted to produce an output indicating an alarm condition and the associated identification component in response to a received alarm signal and an audio and/or visual alarm display means activated by the output of said signal processing means.

Thus with an alarm system of the present invention there is obtained a substantial increase in security by the use of an invisible radio link between the alarm condition sensor and an audio and/or visual alarm display means which can be located entirely remote e.g. many miles away, from the protected property and which cannot readily be interferred with.

Preferably, said local monitoring station and said remote command station each comprise a tranceiver and said local monitoring station is adapted to receive interogation signals from said remote command station and to transmit status signals to said remote command station in response thereto to check, for example if it is operating correctly and/or to reset the individual sensors triggered.

Whilst the local monitoring system could in principle communicate directly with the command means this would in general severely limit the effective area that could be served by a single remote command system. Accordingly the system desirably includes a repeater station, preferably with full duplex capability to permit simultaneous 2-way transmission between the local monitoring station and the remote command means. Most desirably the repeater station is mounted on a communications satellite in a geostationary orbit, in which case the transmitter and receiver means are desirably arranged for operation at ultrahigh frequencies e.g. in the range 1 to 2 GHz.

Further preferred features and advantages of the invention will appear from the following detailed description given by way of example of a preferred embodiment illustrated with reference to the accompanying drawings in which: Fig. 1 is a general schematic block diagram of an alarm system of the invention; Fig. 2 is a more detailed schematic block diagram of the local control means and associated sensors; and Fig. 3 is a similar diagram of the local control interface modem.

Fig. 1 shows a local monitoring station 1 provided with a plurality of sensors 2. The latter can in general be any conventional sensors including for example, temperature sensors, smoke sensors, invisible beam barrier sensors e.g. infra-red or ultra-sonic, pressure mat sensors, sound or pressure wave sensors etc. etc. but in general are desirably arranged to be normally closed circuit type.

Each of the sensors 2 is linked to an alarm processor 3 of a local control system 4 by a hard wired connection 5 or if desired by a radio wave or other invisible substantially interference-free link. The alarm processor 3 monitors the output of the sensors 2 and when it receives an output corresponding to an alarm condition e.g. presence of smoke, produces in turn an output to activate a transceiver 6 to transmit an alarm signal with an identification component 7 the signal having been converted into a form suitable for transmission e.g. a pulse code modulated radio frequency, by a suitable modem 8.

The alarm signal 7 is picked up by a communications satellite 9 in a suitable geostationary orbit and then transmitted to the transceiver 10 of a remote command station 11 wherupon it is reconverted back into digi tal microprocessor-readable logic form by a suitable modem 12. The resulting alarm sig nal is then processed by a signal processing means of a central processing unit 1 3 to produce an output indicating the alarm condition and activating visusal alarm display means such as a printer 14 and/or visual display unit (VDU) 1 5 and an audio alarm display means 1 6 such as an alarm bell or a "999" telephone connection to a police or fire station as appropriate.

The remote command station 11 is capable of producing interrogation signals which can be transmitted to the local monitoring stationl.

The interrogation signals are processed by the alarm processor 3 which can then provide status signals for transmisssion to the remote command station 11 in response thereto. The interrogation signals can be addressed to individual sensors 2 to provide, for example, a check on the operation of the sensor and/or to turn it on or off. To this end intelligent, addressable sensors 2 are provided.

In more detail as shown in Fig. 2 a number of normally closed circuit (N/C) sensors 2, which may be the same or different and which are disposed in different zones of the protected unit or area, are connected to an analyser 17.

The analyser 1 7 is programmed to produce a non-alarm output while the sensors remain in a non-alarm condition.

As soon as one sensor 2 is triggered and goes open-circuit the analyser 1 7 senses this changed condition and the alarm condition sensed and the identity of the sensor triggered are stored in digital code form in a suitable memory e.g. 1 K RAM memory 1 8 linked to the analyser. At this stage the direct output from the analyser which is in the form of a combination of 'high' and 'low' voltage conditions on a series of pins of the analyser microchip connected to the control means output 19, is maintained in non-alarm condition.Once the above information is entered in the memory though, a signal corresponding to the alarm condition and sensor identification in the form of another combination of 'high' and 'low' voltage conditions on those pins, is produced at the control means output 1 9 and is maintained even if the sensor 2 should now be destroyed or otherwise interferred with and will continue to be maintained until the control means is reset by the command means.

The control means also includes a switching logic analyser 20 and associated memory 21 via which a control means input from the transceiver 6 and modem interface 22 are linked to the analyser 1 7 and memory 1 8.

The switching logic analyser 20 is connected to the reset inputs 22 of each sensor 2 for resetting thereof upon receipt of appropriate instructions from the command means 11 and is arranged to erase the memory 1 8 at the same time to remove the details of the last alarm condition detected. The switching logic analyser 20 is also used to set the identification codes of the individual sensors 2, these being held in the memory 1 8 via which they are transmitted to respective sensor inputs 23 so that a predetermined individual identification code is transmitted by the sensor concerned when triggered into an alarm condition.It will be appreciated that this facility for remote resetting is particularly important because in practice many conventional alarms are inactivated after the alarm has been set off so that the property is unprotected until the authorized keyholder is himself able to personally reset the alarm which may not be possible if for example he is on holiday away from home.

The interface modem 8 shown in Fig. 3 includes an alarm processor input 24 for receiving the 'high'-'low' pin combination alarm condition and sensor identification signal from the alarm processor 3 and is linked to a logic converter 25, which converts the 'high'-'low' pin combination into a digitally coded form, and in turn a logic memory 26, which receives and stores the digitally coded information relating to alarm condition and sensor identification until erased upon resetting, and a continual search logic unit 27 which scans the logic memory 26 continuously for receipt of any duly processed alarm condition and identification signals.It will be appreciated from the above that once the alarm condition has been entered in the logic memory 26 this information can continue to be transmitted to the command means even if the alarm processor is subsequently cut off or damaged thereby affording a further degree of security in the system. The search logic unit 27 is linked to a radio frequency tone converter 28 which converts the microprocessor readable digitally coded information of the logic units into a sequentially coded e.g. pulse code modulated wave train which can then be superimposed on or combined with a carrier wave produced by the transceiver which then transmits the resulting coded wave. The search logic unit 27 is also connected to the receiver of the transceiver 6 via a further radio frequency tone converter 28 for receiving and processing signals from the command means 11, and to an output 29 through which duly converted and processed signals received from the command means 11 are passed to the alarm processor 3 e.g. for checking correct operation thereof and/or resetting sensors. It will be appreciated that various modifications may be made to the above described embodiment without departing from the scope of the present invention. Thus, for example, the satellite link could be replaced by a more conventional radio repeater station located on high ground. In addition more than one command station could be provided and/or links therefrom to more than one emergency ser vice unit e.g. police station could be included so that if any one is "busy" for any reason, another could be made aware of the alarm condition and deal with it. Also the repeater could provide an immediate direct link to an authorized person such as the owner e.g. via a bleeper device to advise him of the existence of an alarm condition.

It will be appreciated that the inclusion of a printer can immediately provide a hard copy of the details of the alarm condition e.g. time of alarm, identity of location, identity and position of individual sensor triggered, type of sensor triggered e.g. fire or intruder etc.

thereby further facilitating correct and accurate handling of any alarm condition that might arise.

Claims (8)

1. An alarm system comprising a local monitoring station and a remote command station, wherein the local monitoring station comprises at least one sensor adapted to sense an alarm condition, local control means adapted to monitor the output of said least one sensor and a radio frequency transmitter adapted to transmit an alarm signal with an associated identification component and to be activated by said local control means when an alarm condition is sensed by at least one of said sensors, and the remote command station comprises a radio frequency receiver adapted to receive an alarm signal transmitted by the radio frequency transmitter, signal processing means adapted to produce an output indicating an alarm condition and the associated identification component in response to a received alarm signal and an audio and/or visual alarm display means activated by the output of said signal processing means.

2. An alarm system according to claim 1, wherein said local monitoring station and said remote command station each comprise a tranceiver and said local monitoring station is adapted to receive interrogation signals from said remote command station and to transmit status signals to said remote command station in response thereto.

3. An alarm system according to claim 2, wherein the sensors are intelligent, individually addressable sensors.

4. An alarm system according to claim 2 or 3, wherein said local monitoring station and said remote command station transmit and receive signals at different frequencies to facilitate simultaneous two-way communication therebetween.

5. An alarm system according to any one preceding claim, wherein at least one repeater station is provided between said local monitoring station and said remote command station.

6. An alarm system according to claim 3, wherein said at least one repeater station comprises a communications satellite in geostationary orbit.

7. An alarm system according to claim 6, wherein the operating frequency of the local monitoring station and the remote command means is in the range 1 to 2 GHz.

8. An alarm system substantially as hereinbefore described by way of example with reference to the accompanying drawings.