Alarm System

Abstract

An alarm system for use in conjunction with a radio actuated location system in which a security guard or watchman carries a radio transmitter which transmits signals according to the location of the guard, the alarm system including circuitry to generate an alarm frequency, the guard having a switch (which may operate automatically if he is incapacitated) which, when actuated, causes the alarm frequency to be transmitted (or cut off if it is normally being transmitted).

Description

This invention relates in general to security systems, and more particularly to a system by which a watchman or security guard may instantly give an alarm to a remote monitoring point if he should be attacked or if he should see any untoward circumstance, such as the presence of intruders or a fire.

In order to protect property and maintain a continual watch for the occurrence of fires it is a usual practice to employ a nightwatchman or security guard whose duty it is to patrol the property or premises in question. To ensure that the watchman or guard carries out his duties correctly it is common practice to provide a number of check points all of which the officer in question is required to visit at predetermined intervals. It is known to provide the officer with a clock device which he can actuate by means of keys provided at different locations in order to record each visit to each checkpoint on a paper tape within the clock device. If the officer should be attacked by unauthorized persons lurking on the premises, the fact that he has been attacked and has not visited any of the check points after the attack will not be known until the following morning and the information will then be useless.

In our copending Pat. application Ser. No. 733,675 there is disclosed a system by which the movements of the officer are monitored by radio and each time he reaches one of the check points he connects a plug terminating a cable from the transmitting apparatus he carries to a socket in a wall box at the checkpoint, the wall box containing frequency determining components which, when connected to the transmitter, cause an oscillator to commence operation to generate a particular frequency by which the transmitter carrier wave is modulated. The modulating frequency is detected at the monitoring point and since the modulating frequency produced at each checkpoint is different from those at all the other checkpoints the monitoring apparatus, by recognizing the frequency being received, immediately indicates which point the officer is visiting. If he fails to reach a particular checkpoint at a particular time, or within a few minutes of a particular time, then the correct indication is not shown and it may be assumed that something is wrong. In another of our copending Pat. applications, Ser. No. 733,693 a further system is disclosed which in certain respects is similar to that described above except that in place of the oscillator minus frequency determining components carried by the officer, and the frequency determining components mounted in wall boxes, a series of inductive loops is provided, one at each of the checkpoints, each inductive loop being fitted with a loop generator for generating a modulated carrier. In this case the officer carries a loop aerial and detector and when the officer approaches each inductive loop generator the frequency in question is detected, demodulated and then used to modulate the transmitter carrier. The present invention may be used in conjunction with either of these systems, or with other security location monitoring systems using a radio link.

The invention consists of an alarm system for use in conjunction with a radio actuated security location system comprising means to generate an alarm frequency for application to the modulator of a radio transmitter carried by a security officer who patrols an area to be protected, and a switch to be carried by the officer, the switch being effective to cut off the alarm frequency if it is normally being transmitted or to cause the alarm frequency to be generated and applied to the transmitter modulator if it is not normally being transmitted. The switch is of a type which will produce the alarm condition unless prevented from doing so by a conscious act of the security officer.

Two embodiments of the invention, as applied to the two location systems discussed in the said two copending Pat. applications, will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 shows the application of the invention to a location system as discussed in our copending Pat. application Ser. No. 733,675;

FIG. 2 shows the monitoring system to be used in conjunction with the apparatus shown in FIG. 1; and

FIG. 3 shows the application of the invention to the security location system discussed in our said another copending Pat. application Ser. No. 733,693.

Referring to FIG. 1, there is shown a standard mobile pocket radio transmitter (less microphone) indicated by the dotted rectangle 11. The rectangle 11 contains a block 12 representing the radio transmitter with an aerial 12a having connected to it a transmitter modulator 13. The mobile transmitter may be very small and may be a V.H.F. transmitter of the kind carried by policemen who are on ordinary patrol duties covering different beats. In addition to the transmitting apparatus 11 the officer carries further apparatus indicated by the box 14 containing an oscillator which is not provided with all the usual frequency determining components. The block 14 has leading from it a flexible lead 15 terminating in a jack plug 16 which may be plugged into any one of a number of jacks set in different wall boxes 17 (only one being shown) each of which contains one or more frequency determining component, each box producing a different frequency when connected to the first oscillator circuit in the block 14. The oscillator contained in the block 14 does not oscillate until it is connected to one of the wall boxes 17, when the frequency components are connected so that the oscillator circuit is complete. The apparatus so far described is precisely that described in our said copending Pat. Application Ser. No. 733,675.

According to the invention, the block 14 contains, in addition, a second oscillator circuit which is complete with its frequency determining components and which generates an alarm frequency which is different from all the location frequencies. There is a further flexible lead attached to the block 14 terminating in a switch 18 which is carried by the officer. The switch 18 may be an ordinary pushbutton switch which is either normally open or normally closed, depending upon the particular arrangement adopted in the system. It may, however, be a special type of switch. In that case it is arranged that the switch 18 is normally held either in the open or in the closed position by a spring. For example, the switch may be in the form of a small bulb containing a protrusion upon which the officer must maintain continuous pressure. If he should be threatened or attacked he need only release the pressure to cause the alarm frequency to be transmitted if it is not normally transmitted or to be cut off if it is normally being transmitted, according to the arrangement of the apparatus, which is a matter of choice. If the officer should actually be rendered unconscious he will automatically release the pressure. It will, of course be understood that many kinds of "dead man's switch," as they may be termed, may be devised for use in conjunction with the invention.

The monitoring apparatus comprises a receiver 19 fed by the aerial 19a located at a chosen monitoring point. The output of the receiver 19 is fed to a demodulator 20 which in turn feeds the original modulating frequencies to a series of filters 21. These filters respond to the different location frequencies, and an additional filter responds to the alarm frequency. The location frequencies are fed to an indicating device 22 and if the alarm frequency should either appear (in the case where it should not normally be present) or disappear (in the case where it should normally be present) the change is detected and is used to activate an alarm 23.

In normal use the officer carries out his patrols at the predetermined intervals of time and at each checkpoint inserts the jack plug 16 into the box 17 at that checkpoint. Accordingly the transmitter transmits a continuous carrier wave and from time to time a modulating frequency is detected by the appropriate filter in the block 21 and the indicator 22 is activated to show that the officer has reached the associated checkpoint. However, if the officer should detect intruders or the presence of a fire he need only relax the pressure on the "dead man's switch" which he carries, when the alarm is instantly given at the monitoring point. The alarm switch, is so arranged that if the officer should be the victim of a surprise attack and be rendered helpless or unconscious the alarm switch immediately activates itself in the appropriate direction. It will be evident that although the visits at predetermined times to the checkpoints enable the officer's movements to be continually monitored, the alarm switch enables him to give an immediate alarm indication, wherever he may be. Without the alarm system the person at the monitoring point receives no hint of anything unusual until the next indication fails to appear, and he would then probably wait for a few minutes in case the officer were late. Moreover, if the officer should suddenly be taken ill (and it is quite usual to use elderly men for such duties) or if he should have an accident, the alarm will also be given.

FIG. 3 shows the apparatus required for a system in which the alarm feature of the invention is combined with the invention disclosed in our aforementioned another Pat. application Ser. No. 733,693. It comprises a transmitter indicated by dotted rectangle 11 containing a radio transmitter 12 with an aerial 12a and a modulator 13, as in the transmitter described in relation to FIG. 1. The additional apparatus contained in the block 14 of FIG. 1 is in this case replaced by a block 24 and in place of the numerous wall boxes 17 of FIG. 1 a number of inductive loop frequency generators 25 may each consist of a generator to generate a frequency of, for example, 150 kc./s. which is modulated by a different location frequency at each point in the location system. The block 24 is provided with a loop aerial 26 and it contains a loop detector and a loop demodulator to derive the location frequency provided by any one of the inductive loop generators 25 when the loop aerial 26 is in the proximity of it. In addition, the block 24 contains the oscillator to generate the alarm frequency and has a cable leading to the "dead man's switch" 27, which may be the same as that described in relation to FIG. 1.

The transmitted signal is the same and consists of a carrier which, from time to time, is modulated by one or other of the location frequencies, and where an emergency arises it is modulated by the alarm frequency. Hence, the receiving equipment may be the same as that shown in FIG. 2 for use in conjunction with the transmitting apparatus of FIG. 1.

It will be apparent from the above description of FIGS. 1 and 3, that the two devices each comprise a portable radio transmitter having a modulator 13 and a coupling element, that is the jack plug 16 in FIG. 1 and the loop aerial 26 in FIG. 3, associated with the modulator 13 through, in FIG. 1, the block 14 containing an oscillator not provided with the usual frequency determining components, or, in FIG. 3, the block 24 comprising the loop detector and loop demodulator. In FIG. 1 the coupling element, i.e. plug 16, is movable into and out of electrical coupling association with the stationary wall box 17, the contents comprise one or more frequency determining components, thereby being a frequency-determining conditioning instrument in that, when the plug 16 is in coupling engagement with the wall box 17, the contents of the wall box 17 will cooperate with the contents of the block 14 to apply to the modulator 13 a modulating signal of frequency determined by the frequency-determining conditioning characteristics of the contents of the wall box 17. In FIG. 3, the coupling element, i.e. loop aerial 26, is movable into and out of proximity with the frequency-determining conditioning instrument comprised by the inductive loop frequency generator 25, so that when the parts 26 and 25 are in proximity the generator 25 cooperates with the contents of the block 24 to apply to the modulator 13 a modulating signal frequency determined by the characteristics of the generator 25.

Additionally, in accordance with the invention, an alarm frequency generator comprising in FIG. 1 circuitry in the block 14, or, in FIG. 3 circuitry in the block 24, and the two-state switch 18 or 27 is connected to the alarm frequency generator circuitry to, in one state, switch on the alarm frequency generation and, in the other state, to switch the alarm frequency off. Being under the control of the watchman or other patrol man, he can indicate an emergency by altering the state of the switch.

As explained above, the switch, 18 or 27, is biassed into one state and is adapted to be held by manual pressure in the other state. To indicate an emergency, it is necessary to release the pressure on the switch to permit it to return to the state into which it is biassed and thereby switch the alarm signal on or off.

Claims

We claim:

1. In a portable radio transmitter comprising a modulator and, associated with the modulator, a coupling element which is movable into and out of electrical coupling association with a stationary frequency-determining conditioning instrument to apply to the modulator a modulating signal frequency determined by the frequency-determining conditioning instrument, the provision of an alarm frequency generating circuit coupled to the modulator to generate a radiated alarm frequency, a manually engageable two-state switch connected to the alarm frequency generating circuit to switch on the alarm frequency in one state of the switch and to switch off the alarm frequency in the other state of the switch, and spring biassing means engaging the switch to bias the switch into one state when the switch is manually disengaged.