The present invention relates to an alarm system, in par¬ ticular a community alarm system.

Alarm sensors generating a warning signal in an abnormal situation, such as the occurrence of a burglary, a fire, etc... are positioned in private houses, apartments, offices, etc... The warning signal contains information defining both the nature and the location of the abnormal situation. These known sensors are directly linked to at least one telephone. Such an alarm system is for example described in EP-A 0 484 880. With such known alarm systems there arises, however, the problem that in case of a failure of the associated telephone or the respective telephone lines the warning signal generated by the alarm sensor may not reach a security company, which should be informed in case of an abnormal situation.

It is, therefore, an object of the present invention to develop an alarm system, which even in case of a failure of the telephone connected with the associated alarm sensor guarantees the transmission of the generated warning signal to a security company.

Accordingly the present invention proposes a community alarm system comprising N alarm units, each comprising: a) means for generating a warning signal indicative of an abnormal situation, such as a burglary, a fire, etc. ; b) a telephone associated with the means for generating a warning signal for transmitting a generated warning signal to at least one security company; c) a transceiver means connected with the means for generating the warning signal and the telephone, wherein N is at least 3 or larger and said transceiver means are arranged in a ring network and communicate at least with their direct neighbours in the ring network.

According to the invention a plurality of transceivers form a ring network connecting the alarm systems of clients of a security system responsible for the safety of the afore¬ mentioned properties. This system may exhibit a certain redundancy because a warning signal will be sent to the security company via the telephone directly connected to the means generating the warning signal and the telephones connected to neighbouring transceivers in the ring network. If, however, the telephone line connected to the means generating the warning signal is out of order, the warning signal is still received by the security company, because at least the telephone connected to the neighbouring trans¬ ceiver will send this signal to the security company.

To reduce the redundancy of the inventive system after securing that the warning signal has reached the security company it is proposed according to a preferred embodiment that each telephone after receipt of a signal from the security company reporting a successful transmission of a warning signal emitted from a neighbouring alarm unit sends a signal to the associated transceiver blocking the further transmission of the warning signal to a neighbouring transceiver in the ring network.

To minimize the possibility of a breakdown of a telephone in case of an emergency or an abnormal situation, the community alarm system according to the present invention further comprises means for verifying the condition of the telephone lines associated with each telephone and for sending to the security company an error signal comprising an indication of the location of the line if an abnormal condition is detected for said line. The telephone and the telephone lines used for the transmission of the warning signal is permanently tested. If an abnormal condition, such as a dropout of the line or a line cut, is detected, then a signal indicating the nature and location of said condition is sent to the main security company. This line testing can

be performed by the relevant switch board. Upon detection of the faulty condition, the security company is automatically informed and a request for repairing the line and/or the resepective telephone is generated.

The community alarm system would fail to function if a warning signal is generated and, because of a defect in the telephone line dircetly connected with the means for generating said warning signal, said signal is sent to the telephone connected with the neighbouring transceiver and said telephone is engaged. Indeed, in this case no warning signal can be sent to the security company since the telephones are either disconnected or blocked. To avoid this problem, the community alarm system according to a preferred embodiment further comprises means for generating a signal indicating an off-hook or disconnected condition of a tele¬ phone. Each telephone is connected with such a detector.

According to preferred embodiment the community alarm system according to the present invention further comprises switches between each of the transceivers and the telephones to transmit a received warning signal to the next trans¬ ceiver if the telephone connected to the transceiver re¬ ceiving the warning signal is off-hook or disconnected and to transmit the received warning signal to the telephone connected to said transceiver if said telephones is not off- hook. The output of a detector activates a corresponding switch. If an off hook condition is detected for one of the telephones connected to a transceiver, then an incoming warning signal is transmitted to the neighbouring trans¬ ceiver in the ring network rather than to a telephone of said transceiver.

For enabling a quick response to an abnormal situation according to a preferred embodiment the warning signal comprises an indication of the nature and location of the abnormal situation. In different abnormal situations it may

further be useful to alarm different security companies or relief companies. To solve this problem the community alarm system according to the present invention is further improved in that depending on the nature of the warning signal each telephone is transmitting the warning signal to different security companies.

To detect a possible breakdown in any of the transceivers the community alarm system according to the present inven- tion further comprises means for detecting a defect in one of the transceiver means and means for sending a signal indicating the nature and location of said defect to at least one of the security companies. According to the inven¬ tion a series of pulses is sent around the ring network of ransceivers. The transmitter sends on the pulses received by the according receiver of the transmitter. If the con¬ nection between two transceivers breaks down (because of a defect in the transmitter of the first or the receiver in the second transceiver or a blockage of the link) , the second transceiver will not receive pulses and can, there¬ fore, not send out pulses. As a result, every following receiver in the network cannot receive any pulses and will send an error message to the central security company. Therefore, to determine between which of two neighbouring transceivers the link failed, the series of pulses are statistically sent either in the first or the second direction of the ring. The failure is then located between the two neighbouring transceivers of which one sends an error message to the security company in one direction and the other one sends an error message to the security company for pulses travelling in the opposite direction.

If apart from the location of the failing link, also a determination of the nature of the error is desirable, then the series of pulses are to be continously sent in both directions. Suppose there are three transceivers A, B and C.

The pulses are sent between the transceivers as indicated in the following diagram:

The defects in the transmitter or receiver of one of the transceivers or the presence of an obstacle in the path forming the link between two transceivers can be determined according to the scenario to be followed in case e.g. trans¬ ceiver B fails to receive a pulse from transceiver A or C:

If B does not receive

And B does not receive

But C receives

Or A receives

Then the receiver of B is defect.

If B does not receive

But B receives

And A receives B

Then the transmitter of A is defect.

If B does not receive A

And A does not receive B

But B receives C

And A receives C

Then the link between A and B is disturbed

This scenario can easily be extrapolated for a defect in any of the transmitters, receivers or a blockage in the link between two neighbouring transceivers and for any number of transceivers in a common ring network.

Furthermore, to prevent a burglar from stopping a warning signal being sent around the ring without this defect being noticed by the security company, e.g. by replacing the transmitter of a transceiver by a source continously generating pulses, the pulses sent around the ring network of transceivers are coded or preceded by a code word ac¬ cording to a preferred embodiment of the inventive community alarm system.

A possible malfunctioning of the means for generating a warning signal can be detected by regularly simulating an alarm condition and verifying whether a warning signal is received at the central security company. In this case the community alarm system according to the present invention comprises means for detecting a defect in the means for generating a warning signal and means for sending a signal indicating the nature and location of the defect to the security company. For e.g. an infrared burglary alarm an object is interposed between the source and the detector of the alarm. If no warning signal is received at the security company, and no error signals for the transceivers or the

telephone lines were received, then it can be assumed that the means for generating a warning signal are defect.

By assuring that neighbouring transceivers on the ring network are not connected to telephones sharing a common trunk cable going to the local switch board, the security of the inventive ccjmmunity alarm system can be further en¬ hanced. Indeed, if said trunk is cut, the warning signal is still sent to the security company via the telephone of the neighbouring transceiver, because the telephone connected to said transceiver is net connected to a line of said trunk cable.

For alarming the immediate neighbourhood in case of an abnormal situation the means for generating a warning signal is further coupled with means for generating optical and/or acoustical warning signals according to a further preferred embodiment.

The foregoing and other objects and features of the present invention will also become appearent from the following description of an exemplary embodiment of the community alarm system according to the present invention, which is shown in the accompanying drawing.

Figure 1 shows an embodiment of the present invention com¬ prising a ring network 10 with four transceivers 12. Each transceiver 12 is coupled with a generator 20 for generating a warning signal in case of an abnormal situation. Between each transceiver 12 and the according telephone 30 and bet¬ ween two neighbouring transceivers 12 a switch 50 is actuated upon receipt of a warning signal and in dependency on the output signal of an off-hook detector 60. Such switch 50 is positioned between each two neighbouring transceivers 12. For sake of simplicity of the drawing, however, only one such switch 50 is shown. If the detector 60 detects a situation, in which the according telephone 30 is engaged or

blocked, a warning signal resulting from a neighbouring alarm unit by-passes the respective transceiver 12 and is transmitted to the next transceiver 12 of the ring network 10 to guarantee a transmission of the warning signal to a central security company 40 connected to the alarm units via the telephones 30.

The warning signal generator 20 of each alarm unit is connected to both a telephone 30 and a transceiver 12. The telephone lines 32 are tested by the telephone switch board 36 using means 34. The signals from the warning signal generator 20 or from the means 45 detecting defects in the system are sent to the security company 40. The means 45 for detecting defects in the ring network 10 sends coded pulses to prevent an intruder from manipulating the community alarm system. For further enhancing the security of the community alarm system the telephones 30 of the system are connected to different trunk cables going to the local switch board 36 as is schemtically shown for the left and bottom alarm units of Fig. 1.

Additionally the warning signal generator 20 is coupled with means 25 for generating optical and/or acoustical warning signals. For sake of simplicity only one such means 25 for generating optical and/or acoustical warning signals is shown in the drawing.

Depending on the nature of the generated warning signal the telephones are linked with the central security company 40 and/or additional security companies 41 and 42, which may be specialised for different emergency cases. For example, it may be useful to inform in case of a fire first of all the fire brigade, whereas in case of a burglary it should be useful to inform the police station first.