EP0547458B1 - Radio alarm system - Google Patents

Abstract

A radio alarm system is described which consists of a central station (1) with a receiving unit (2), a computer unit (3) and a transmitting unit (8) and of at least one detector (4) with a transmitting unit (7), computer unit (6), a signalling unit (5) and a receiving unit (12). The receiving units of the central station and of the detector are tuned to the respective transmitting units. In the case of an event, the transmitting unit (7) of the detector (4) outputs a first radio signal to the central station which is received by its receiving unit (2) and in the latter initiates, in a manner for generating a request signal for repeating the first radio signal from the detector (4), that a random-number generator generates a code which is stored in the memory of the computer unit (3) and is used for processing the radio signal which is radiated by the central station. The radio signal is received by the detector (4), forwarded to its computer unit which prepares the repeated signal using the code also received from the central station (1) and which is then radiated by the transmitting unit (7). The receiving unit (2) of the central station (1) receives the repeated signal and forwards it to its computer unit (3) in which the received code is filtered out and compared with the code stored in its memory. If the received code deviates from the stored code, a fault alarm is generated by the central station whereas when both codes are identical, the signal is processed in accordance with its content and the state of the central station. <IMAGE>

Description

Alarm systems or alarm systems are used to secure and monitor buildings, objects or the like. Alarm systems or systems of this type, such as are described, for example, in US Pat. No. 4,511,887 or US Pat. No. 4,603,325, consist in any case of a control center, the so-called alarm center, and various detectors, such as opening detectors or motion detectors and the so-called alarm transmitters, such as outdoor and indoor sirens or strobe lights. In addition, transmission facilities are part of such systems, which in the event of a report forward the information via telephone lines to a constantly manned security service or to police stations. The alarm centers with the respective detectors, arming devices and alarm devices form a self-contained unit with functionally coordinated system components, which guarantee the function maintenance of the system in any case and at the same time prevent tampering from unauthorized parties, even from outside the closed system. can be made. In the case of wired systems, manipulation from the outside is impossible or very difficult if all system components with the exception of the alarm device, the external siren and strobe lights are located within the enclosed space. Tampering with the external system parts is also very difficult since the housings of the alarm devices are secured by tamper contacts or similar signaling devices that respond to unauthorized manipulation. This applies without restriction to wired alarm systems.

With wireless alarm systems, and especially with wireless alarm systems that work with radio transmission devices, it is very easy to manipulate from the outside, since the radio signals also pass through the walls of the enclosed space. To show the possibility of manipulation, a typical radio alarm system is described with reference to FIG. 2.

The radio alarm center according to FIG. 2 consists of the control unit 20a, a voltage supply device 20b, a radio receiver 20c and a radio transmitter 20d. An infrared motion detector 21a is connected to a voltage supply device 21b and to a radio transmitter 21c. In the event of an alarm event, the motion detector 21a issues a control command to the radio transmitter 21c. The latter then sends a so-called data telegram to the radio receiver 20c. The wireless alarm center handles the further processing.

The same applies to an opening contact 22a, for example on a door, which is connected to a voltage supply device 22b and a radio transmitter 22c. To lock the system, a bolt switch lock 23a is used, which is connected to a mechanical blocking element 23e, a radio transmitter 23c, control electronics 23d and a voltage supply device 23b. In the case of arming, a radio pulse is emitted to the radio receiver 20c of the alarm center via the radio transmitter 23c, whereupon the system is activated.

Furthermore, a telephone dialing device 24a is provided, which is connected to a radio receiver 24c, a voltage supply device 24b (for example a power supply unit with a battery emergency power supply) and to a radio transmitter 24d. In the event of an alarm, the central station controls the radio transmitter 20d, which emits a radio signal to the radio receiver 24c. This radio receiver 24c controls the telephone dialer 24a via an output. The same applies to the radio transmitter 24d: this transmits a sabotage message to the radio receiver 20c of the alarm center.

Finally, an external siren 25a is provided, which is connected to control electronics 25d, a voltage supply device 25b, a radio receiver 25c and a radio transmitter 25e. In the event of an alarm, the external siren 25a receives a signal via the radio transmitter 20d and the receiver 25c. The receiver 25c controls the external siren 25a via the control electronics 25d. The radio transmitter 25e is used to transmit a sabotage message to the radio receiver 20c of the alarm center.

In order to clarify the basic functional sequence of radio transmission within the alarm system, reference is made to FIG. 3.

A detector 30 opens or closes its alarm contact and thus controls a switching logic 31. The same applies to a battery monitor 32 and a sabotage monitor 33. A fixed coding, which is set, for example, with dip-switch switches or can also be hard-wired, is modulated together with the switching states in a modulation stage 34 and via the transmitter 35 as already mentioned data telegram sent. This data telegram is received by the receiver 36 and demodulated in the demodulation stage 41. In order to adapt the receiver 36 to the transmitter in terms of coding, it is also possible here to work either with dip-switch switches or with hard wiring. If the data telegram is recognized as valid, the switching logic 42 controls the outputs 38, 39 or 40, for example. Usually 10 bits are used for transmitter identification (coding), so that 1024 codings are possible.

The patents mentioned at the outset have various special functions:

The alarm system according to US Pat. No. 4,511,887 can also be operated as a two-way system, the control center sending out a request signal which is answered by the addressed detector after a period of time which characterizes it.

Such a request signal is also known from US-A-4,477,800.

In the system according to US Pat. No. 4,603,325, the signal field strength of the individual detectors is recorded, but not in order to detect manipulations, but in order to find radiation-friendly locations for the transmitters when installing the system.

As can be seen from the above illustration, it is possible to find out the correct coding from the outside with appropriate technical equipment, but also with a structurally identical transmission unit, by trying out all possible coding options and thus to achieve faults or alarm triggers. It is also possible, with suitable technical equipment, to wait for a radio signal from a signaling unit of the monitored object and to do so to register. This registered signal can then be sent back by the technical device and thus used for manipulation, since the receiving device of the control center recognizes the signal as valid.

Against the background shown, it is the object of the present invention to provide a radio alarm system which cannot be manipulated from the outside in any way, even if a person attempting the manipulation has technical receiving and transmitting devices which are capable of doing so To receive, record and send radio signals from the system to be manipulated. A partial solution to this problem is already known from US-A-3,713,142. However, it requires a regular broadcast of random codes: if all codes and their answers are listened to, manipulation is possible.

This object is achieved by a radio alarm system with the features of claim 1. Further advantageous developments are specified in the subclaims.

The radio alarm system consists of a control center which has a receiving unit, a computer unit and a transmitting unit, and at least one detector which has a transmitting unit, a computer unit, a reporting unit and a receiving unit. The signaling unit can be a motion detector, for example.

The reception unit of the control center is matched to the radio signal or radio signals of the transmitter unit of the detector and accordingly the reception unit of the detector to the radio signal or radio signals of the transmitter unit of the control center.

In the event of an event in which, for example, the detector designed as a motion detector is one Sends the message, the transmitter unit of the detector sends a first radio signal to the control center. The signal is received by their receiving unit, whereupon the central unit triggers the generation of a request signal for the detector to repeat the first radio signal. This is done in such a way that a random generator generates a code in the control center, which code is stored in the memory of the processing unit of the control center and is used for the signal form and the signal content of the radio signal representing the request signal. The latter is then emitted by the central control unit.

The radio signal emitted by the control center is received by the detector's receiving unit and passed on to its computer unit, whereupon the latter prepares the repeat signal of the first radio signal using or processing the code received by the control center. The transmitter unit of the detector then emits the repeat signal to the control center.

The reception unit of the control center then receives the repeat signal and forwards it to the computer unit, in which the received code is filtered out of the signal and compared with the code previously stored in its memory. If the received code differs from the stored code, a fault alarm signal is generated by the control center, whereas if both codes are identical, the message is processed in accordance with its content and the status of the control center, since it is then certain that the message has not occurred arbitrarily or accidentally.

A possibility of manipulation from the outside is with the The radio alarm system according to the invention is therefore excluded in that the request signal for repetition of the first radio signal is given a randomly selected code by the detector, which code is sent back by the detector in the repeat signal back to the control center, in which the correspondence of the received code with the expected code is checked. It is of no use in a manipulation attempt, for example to receive the request signal from the control center from the outside with a high level of technical complexity and to generate a corresponding repetition signal, since the time period for determining and evaluating as well as for generating such a signal is much too long to be confirmed - or to send a repeat signal before the system's own detector has already done so. The control center will issue a different code for the next message event.

According to an advantageous development, the security of the system can be increased further in that the random generator generates a number as a code with which an algorithm function stored in the computer unit of the central unit is calculated and the result of this calculation is stored in the memory of this computer unit of the central unit. The code is again transmitted to the detector with the request signal for repeating the first radio signal, in whose computer unit the same algorhithmic function is stored with which the received function is used to calculate the same function. The result is radioed to the control center together with the repeat signal of the first radio signal. The central processing unit then compares the calculation result with the result stored in it.

The algorithmic function itself can also be the result of a random process, which further increases security. For example, the coefficients of a polynomial can first be generated by the random generator.

However, the code can also be a sequence of alphanumeric characters, with depths of up to 100 bits being technically feasible without any problems.

The code can precede the data telegrams contained in the radio signals or, alternatively, the code itself can influence the structure of the data telegrams contained in the radio signals, for example by convolution, multiplication or the like.

If the alarm system has several detectors and if several messages from different detectors are received by the control center at the same time or at the same time, the incoming message from a detector is first processed by the control center in the manner described. All other incoming messages are buffered and processed one after the other.

If the detector does not receive a request signal from the control center for repeating the radio signal which it first emits, then, according to an advantageous development, it again sends its first radio signal within a certain time interval. This can be repeated until a request signal from the control center is registered in the detector.

On the other hand, if the repeat signal is a According to an advantageous development, the control center requests the detector for the second time to send a repeat signal to the control center, which has previously sent a message to the control center. Here, the control center sends a new code in order to exclude the possibility of manipulation by analyzing the first request signal and by simulating a corresponding repetition signal. If the newly requested repeat signal fails to appear, the control center must assume that an attempt to tamper with an identical detector has been attempted, which is why the control center then - if it is armed - for example an alarm message or - if it is unset - for Example triggers a fault message.

Alternatively, the control center can assume that the detector is defective and proceed in the same way as it would if a manipulation attempt were accepted.

According to an advantageous development, the control center informs the detector of its switching state by means of a radio signal, that is to say whether it is switched on or off. An advantage here arises from the fact that in the unset state of the control panel a detector does not have to react to an event and the battery capacity which is used to supply the detector with power is not unnecessarily used up. A program in the detector's computer unit differentiates between a message that his message unit triggers based on its physical mode of action and messages that are triggered, for example, by sabotage contacts or Battery failures arise. In the first case, the detector only issues a message if the control panel is in an armed state and has informed the detector. In the second case, messages are always issued by the detector, since an attempted sabotage, a battery fault, or another message is evident.

An identification code can be assigned to each detector, which is also transmitted with each radio signal. This identification code is then stored in advance in the memory of the computer unit of the control center during the commissioning of the system. When a radio signal is received from a detector, the belonging of the detector to the radio alarm system is checked by comparing the incoming identification code with the stored identification code. If the two codes are not identical, a corresponding signal is triggered, which indicates this fact.

The identification code specific to each detector can also be used for coding the repetition signal, for example in such a way that the identification code specifically processes the random code received from the control center. For example, the identification code could specify the coefficients of a polynomial to be calculated.

The identification code of each detector stored in the control center can be sent with the request signal from the control center to the addressed detector, so that the corresponding detector "knows" that only it is addressed.

Figur 1:

ein schematisches Blockdiagramm einer Alarmanlage aus einer Zentrale und einem Melder.

The invention is explained in more detail using an exemplary embodiment. Here shows:

Figure 1:

a schematic block diagram of an alarm system from a control center and a detector.

The radio alarm system consists of a control center 1 with the integrated components receiving unit 2, computing unit 3 and transmitting unit 8. The detector 4 has the components reporting unit 5, computing unit 6, transmitting unit 7 and receiving unit 12.

If a differentiated temperature change is ascertained by the signaling unit 5, for example a passive infrared motion detector, according to its physical mode of operation, this message is passed on to the computer unit 6 and processed by it, a data telegram is prepared and the modulation is then prepared for the transmission unit 7 . The transmitting unit 7 then sends a data telegram to the receiving unit 2 of the control center 1. The receiving unit 2 receives this data telegram and forwards it to the computer unit 3 of the control center 1, where it is processed and evaluated. After the evaluation, the computer unit 3 randomly determines a number or a sequence of numbers, compiles a data telegram and carries out the modulation for the transmission unit 8 and then sends a request signal for repeating the first radio signal to the detector 4. This request signal is received by the receiving unit 12 of the detector 4 and processed in the computer unit 6, the The number or sequence of numbers supplied, which was generated at random by the computer unit in the control center, is used to be used in an algorhithmic function that has been programmed into the computer unit 6, the computer unit 6 performing this algorhithmic function with the aid of this number resolves and includes the result in the confirmation message sent by the transmitter unit 7. Since the computer unit 3 of the central unit 1 has programmed the same algorithmic function and has already carried out the same calculation and has stored the result in a memory, this computer unit 3 expects a defined one-time data telegram from the detector, including the number previously sent.

Instead of an algorithmic function, a sequence of numbers or a sequence of letters can also be programmed into the computer unit, so that the number which is determined by the computer unit purely by chance indicates, for example, a position or number in a programmed sequence of numbers or letters. The number that was determined by the computer unit 3 at random can also continue to be used to change the bit sequence of the data telegram, which is generated by the computer unit 6 of the detector, according to certain predetermined patterns. The simplest way of using the number determined by the computer unit 3 of the control center 1 by random principle is to have the number used directly by the computer unit 6 of the detector.

The respective radio links between the control center 1 and referred to the detector 4. In the event of an event, a first radio signal is sent from the detector 4 to the control center 1 on the radio link 9. The request signal is transmitted from the control center 1 on the radio link 10 to repeat the first radio signal from the detector 4. Finally, the radio link 11 is provided for transmitting the repetition signal of the first radio signal from the detector to the control center.

Claims (12)

1. Radio alarm system, comprising

   - a central unit (1), which has a receiver (2), a computer (3) and a transmitter (8), and

   - at least one alarm box (4) which has a transmitter (7), a computer (6), a signalling unit (5) and a receiver (12),

   whereby

   - the receiver (2) of the central unit (1) is tuned to the radio signal of the transmitter (7) of the alarm box (4) and correspondingly the receiver (2) of the alarm box (4) is tuned to the radio signal of the central unit (1)

   with which

   - the transmitter (7) of the alarm box (4), in the case of an event, delivers a first radio signal (9) to the central unit (1) which is picked up by its receiver (2) and in this triggers the generation of a request signal (10) for repetition of the first radio signal from the alarm box (4), characterized in that, for the generation of the request signal, a random generator produces a code which is deposited in the store of the computer (3) of the central unit and is consulted for the signal shape and the signal content of the radio signal representing the request signal, which is emitted by the transmitter (8) of the central unit (1),

   - the receiver (12) of the alarm box (4) picks up the radio signal, forwards it to its computer (6), this prepares the signal for repetition of the first radio signal by using or processing the code also received from the central unit (1), which signal the transmitter (7) of the alarm box (4) then emits to the central unit (1),

   - the receiver (2) of the central unit (1) receives the repeat signal (11) and passes it on to its computer (3) in which the received code is filtered out from the signal and compared with the code deposited in its store,

   - with detection of a difference between the received code and the stored code, a fault alarm signal is generated by the central unit (1), whereas

   - if the two codes are identical, the communication is processed according to its content and the status of the central unit (1).
2. Radio alarm system according to Claim 1, with which the random generator produces a number as a code, with which an algorithmic function stored in the computer (3) is computed and the result of this computation is deposited in the store of the computer (3) and with which in the computer (6) of the alarm box (4) the same algorithmic function is computed with the received code.
3. Radio alarm system according to Claim 2, with which the algorithmic function is itself the result of a random process.
4. Radio alarm system according to Claim 1, with which the code is a sequence of alphanumeric characters.
5. Radio alarm system according to one of Claims 1 to 4, with which the code is placed in front of the data telegrams contained in the radio signals.
6. Radio alarm system according to one of Claims 1 to 4, with which the code itself determines the structure of the data telegrams contained in the radio signals.
7. Radio alarm system according to one of Claims 1 to 6, with which the alarm box (4), in the case of non-reception of the request signal from the central unit (1) within a certain interval of time, again transmits its first radio signal.
8. Radio alarm system according to one of Claims 1 to 7, with which the central unit (1) in the case of non-reception of the repetition of the first radio signal from the alarm box (4) again emits a request signal with a new code, whereby in the case of continued non-reception of a radio signal from the alarm box (4), depending on the switch status of the central unit (1), an alarm is triggered.
9. Radio alarm system according to one of Claims 1 to 8, with which the central unit (1) notifies the alarm box (4) of its switch status by means of a radio signal.
10. Radio alarm system according to one of Claims 1 to 9, with which an identification code is assigned to the alarm box (4), this identification code being transmitted along with each radio signal, with which the identification code is stored in the store of the computer (3) of the central unit (1) and on reception of a radio signal the fact that the alarm box (4) belongs to the radio alarm system is checked by comparison of the incoming identification code with the stored identification code and, if they are not identical, a corresponding signal is given.
11. Radio alarm system according to Claim 10, with which the identification code of the alarm box (4) is referred to for processing the random code produced by the central unit (1).
12. Radio alarm system according to Claim 10 or 11, with which the central unit (1) sends, along with the request signal for repetition of the first radio signal, the identification code of that alarm box (4) which transmitted the first radio signal.

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