GB2102607A

GB2102607A - Improvements in alarms

Info

Publication number: GB2102607A
Application number: GB08122860A
Authority: GB
Inventors: Robert Armstrong
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-07-24
Filing date: 1981-07-24
Publication date: 1983-02-02
Also published as: GB2102607B

Abstract

A personal alarm system is contained in a box (10) which may be exposed or concealed. A "set" button (S1) starts a timer which sets off an alarm after a suitable delay unless in the meantime a concealed "cancel" button (S3) is operated to reset the timer. A light emitting diode (LED 1) is switched on while the timer is timing out. A key-operated "reset" switch (S2) is provided for switching off the alarm which, once started, cannot be switched off by means of the "set" or "cancel" button. <IMAGE>

Description

SPECIFICATION Improvements in alarms The present invention relates to personal alarm systems.

With the use of known personal alarm systems, it is necessary for a person who is being threatened with violence to press a button or throw a switch to set off the alarm. This is not very satisfactory as the attacker can prevent his victim from setting off the alarm.

It is an object of the present invention to provide a personal alarm which can be set to go off automati cally in the case of a personal attack.

According to the present invention, a personal alarm system comprises alarm switch means adapted, when activated, to operate an alarm, a timer for activating the alarm switch means when the timer has timed out, a "set" switch for starting the timer, and a "cancel" switch for re-setting the timer before it has timed out.

In use, a person at risk, i.e. a potential victim of physical violence, e.g. when about to answerthe door to a caller, operates the set switch to set the timer, so that the alarm is raised automatically when the timer has timed out unless, in the meantime the person at risk has satisfied himself or herself that there is no danger and operates the cancel switch so that the alarm is not raised.

Preferably, the cancel switch is located in a concealed position, remote from the remainder of the alarm system. A further switch, preferably keyoperated, can be provided such that the alarm, once it has been raised, cannot be switched off without the use of the key.

The invention is further described, by way of example, with reference to the drawings, in which: Fig. 1 is a somewhat diagrammatic illustration of a personal alarm system in accordance with the invention; Fig. 2 is a circuit diagram of one embodiment of the alarm system; and Fig. 3 is a circuit diagram of another embodiment of the alarm system.

The circuitry of the alarm system according to the present invention is principally contained in a box 10 made of steel or other suitable material. The circuitry includes a push button switch S1 for setting the time which is pre-adjusted to a suitable time interval lying, for example, between 1 second and 200 seconds according to individual requirements. The circuitry is such that if the timer is timed out the alarm is automatically set off. The alarm can be prevented from being set off by operating a push button cancel switch S3 before the timer has timed out. Operating the switch S3 both resets the timer for future use and prevents the alarm from going off.

The alarm system may incorporate its own alarm bell or siren so that it is wholly self-contained. Alternatively or additionally, it may be adapted to set off a conventional burglar alarm.

In use the box 10 may be placed near an outside door or a short distance from an outside door. It may be conspicuously placed or concealed from view according to individual wishes. Operation of the switch S1 illuminates a light emitting diode LED1 which indicates that the alarm will go off unless the switch S3 is operated before the timer has timed out.

The switch S3 will normally be in a concealed position remote from the box and the wiring between the switch and the box will also normally be concealed.

Thus, the routine when the system is instailed in a dwelling of a person exposed to the risk of personal attack, particularly an elderly person, is for that person before answering the doorto operate the set switch S1. Illumination of the light emitting diode LED1 will indicate that the timer is operating. That person then answers the door and after satisfying himself or herself that all is well he or she operates the concealed cancel switch S3 to prevent the alarm from going off. Should the person answering the door be threatened or feel threatened, the cancel switch S3 remains unoperated and after the timer has timed outthe alarm is raised.The attacker or potentiai attacker cannot prevent the alarm from being raised nor cancel the alarm since the attacker will not know where the cancel switch S3 is situated and will not have the key to operate the key-operated switch S2 which is provided on the box 10 for the purpose of switching off the alarm.

The box 10 will normally contain its own battery and a test button (not shown) may be provided for testing the battery. This test button would normally immediately operate the alarm while held depressed but in this case the provision of a test button would not be suitable if the alarm system is connected to an alarm in a police station.

Referring now to Fig. 2 of the drawings terminals 1 and 2 are connected to a battery preferably of twelve volts. The positive terminal 1 is connected to a positive lead 11 via a diode D6 which is a protective diodeforpreventingthecircuitryfrom being damaged should be battery be connected with the wrong polarity. An output relay RLA is connected to the collector of an output transistor J1, this series circuit being connected between the positive lead 11 and a negative or earth lead 12 which is connected to the battery terminal 2. The relay RLA has a normally open contact Al which is connected in series with output terminals 8, 9, this series circuit being connected between the battery terminals 1 and 2.The terminals 8 and 9 are connected to a suitably disposed alarm bell or siren which may be disposed within the box 10 of Fig. 1 or may be arranged separately e.g. on the outside of the dwelling house. The relay RLA also has a changeover contact A2 connected to terminals 3,4 and 5 which may be wired into a separate alarm system such as a burglar alarm system which may be already fitted to the dwelling or which may have connection lines to a police station.

The positive lead 11 is connected via diode D4to an extension lead 11a and a voltage stabilizing capacitor C1 is connected between the lead portion llaandtheearth lead 12. The purpose ofthe capacitor C1 and the diode D4 is to prevent a tem porary drop in voltage on the lead portion 11 a when an inductive load, i.e. the relay RLA and the alarm bell itself, is connected to the positive lead 11.

The circuitry contains a bistable flip-flop It1 a and lClbwhichforms part of the timer which also includes an electrolytic capacitor C2 and an adjust able discharging resistor RV1. In the quiescent or steady state with the alarm system inoperative the capacitor C2 is rapidly charged through resistor R4 and diode D1. When the set switch S1 is operated it changes over the bistable flip-flop whereby the resistor R4 instead of being connected to the positive lead 1 lea is connected to earth so that the timer capacitor C2 discharges through the resistor Rev1, the diode D1 operating to short circuit the resistor RV1 during charging of the capacitor but being blocked during discharge.

The capacitor C2 is connected to a Schmidt trigger lCl c which is tripped when the timer is timed out i.e.

when the capacitor C2 has discharged to a sufficiently low voltage. In the steady state the output of the Schmidt trigger ICle is zero and this output is passed via a resistor R9 to the base of the output transistor J2 so that the latter is normally blocked.

When the Schmidt trigger IC1 c is fired the transistor J2 becomes conductive to pull in the relay RLA and set off the alarm.

The cancel switch S3 is connected between the output of the Schmidt trigger ICic and the reset input ofthe bistableflip-flop ICla and ICib. Closing of the cancel switch 53 resets the bistable flip-flop so recharging the capacitor C2 and preventing the timer from timing out.

The reset input to the bistable flip-flop is connected to the junction between resistors R2 and R3 which are connected in series with the key switch S2 which is a normally closed switch. In order to cancel the alarm once the relay RLA has operated the key switch S2 is opened in order to apply a zero signal to the reset input of the bistable flip-flop thereby resetting the latter so that a zero output once again appears and switches off the output transistor J2. At the same time the timer capacitor is recharged through the resistor R4 and the diode D1.

A diode D5 is connected in parallel with the relay RLA for the purpose of conducting transients which are induced when the relay is switched off. A light emitting diode LED2 in series with a resistor R12 is also connected to the collector of the output transistor J2 so that this light emitting diode is illuminated when the alarm is raised. The light emitting diode LED2 is not shown in Fig. 1 but may be provided to indicate that the alarm is sounding when the alarm cannot be heard or seen by the person using the alarm system.

The outputs of the Schmidt trigger IC1c and the bistableflip-flop ICla and IClb are connected by respective gating diodes D2 and D3 to an electronic switch ICld whose output is connected via a resistor R10 to the base of a transistor Ji. The collector of the transitor J1 is connected via a resistor Rl 1 to the light emitting diode LEDi. As soon as the bistable flip-flop is changed over by closing the switch S1 or otherwise the transistor J1 becomes conductive to cause the light emitting diode LED1 to light up.

Immediately the timer is timed out the light emitting diode LEDl is extinguished.

The resistor R4 is of relatively low resistance to ensure that the capacitor C2 can be rapidly recharged. The purpose of th is resistor is to limit the current applied to the output of the bistableflip-flop and to the input of the Schmidt trigger ICi c when the battery is disconnected.

The junction of resistors 6 and 7 is connected to the reference input to the Schmidt trigger IC1 c and these resistors are connected in series with terminals 6 and 7 which are connected to a normally closed switch or several normally closed switches connected in series. Such switches may be remotely situated and can be operated at any time to raise the alarm since operation of any one of these switches will cause the application of a zero signal to the reference input of the Schmidt trigger thereby firing the Schmidt trigger and operating the relay RLA. In the event that such remote switches are not installed the terminals 6 and 7 must be strapped together. The remote switches when fitted are preferably not push button switches since the alarm will only remain operated so long as one of these switches is held open.As soon as the series circuit through the resistors R6 and R7 is completed a positive signal is again applied to the reference input of the Schmidt trigger.

Various changes may be made to the circuit. For example, the bistableflip-flop ICla and IC1b replaced by a Schmidt trigger. However, it is preferred to use a MOS integrated circuit since such a circuit can be designed to produce a quiescent current drain from the battery of the order of 30 1LA. The current taken by a system other than thatforthe alarm is about 15mA. In the case wherein an internal bell or siren is fitted this will take a current of about 1A.

Fig. 3 of the drawings illustrates another embodiment of alarm system in which a greater use is made of relays. In this embodiment the set switch S1 is connected in series with the cancel switch S3 and with contacts El of a relay RLE. This series circuit of switches and contacts is connected in series with a relay RLB which has a hold contact B1 in parallel with the switch S1. Thus, the relay RLB pulls in and holds when the alarm is set and is released when the alarm is cancelled before the timer times out.The series circuit of switches and contacts B1 and S3 is also connected to the timer which comprises a transistor J4 as well as the capacitor C2 and adjuster resistor RV1. The transistor J4 receives its input through base resistors R13 and R14 and its collector is connected to the positive lead 11 via a load resistor R22 and to the capacitor C2 via the resistor RV1 shunted by the diode D1 and the current limiting resistor R4. The capacitor C2 is connected via a diode D7 to an amplifier IC1 whose output is connected to the relay RLE. The amplifier IC1 is also connected to the series circuit comprising the contact B1 and the switch S3 so that the relay RLE is released immediately the switch S3 is opened. The changeover contact El of relay RLE maintains the power connection to this relay via the key operated switch S2 but releases the relay RLB. Normally closed contact E2 of relay RLE in the quiescent state holds a control trans isto r J3 blocked whereby the output transistor 52 in series with the relay RLA is also blocked. When the relay RLE is energized the transistor J2 becomes conductive to operate the relay RLA.

In the embodiment of Fig. 3 the light emitting diode LED1 is connected in parallel with the relay RLB so that this light emitting diode is switched on when the set switch is closed and the timer is operating but is extinguished again as soon as the timer has timed out and the alarm is raised.

in other respects the circuit of Fig. 3 operates in the same manner as Fig. 2 and like parts are denoted by like reference numerals.

As indicated in Fig. 2 by dotted lines, capacitors C3 and C4 can be connected in parallel with the resistors R7 and R3 lying at the input sides of the Schmidt trigger IC1c and the bistableflip-flow IC1a/lC1 b, respectively. These capacitors prevent interference which may be present on the leads 11 and 12 from reaching the respective circuit components.

Claims

1. A personal alarm system which comprises alarm switch means adapted, when activated, to operate an alarm, a timer for activating the alarm switch means when the timer has timed out, a "set" switch for starting the timer, and a "cancel" swtich for re-setting the timer before it has timed out.

2. An alarm system as claimed in claim 1, in which the cancel switch is located in a concealed position, remote from the remainder of the alarm system.

3. An alarm system as claimed in claim 1, in which a further switch is provided such that the alarm, once it has been raised, can only be switched off by operating that further switch.

4. An alarm system as claimed in claim 3, in which said further switch is key-operated.

5. An alarm system as claimed in any preceding claim, which has a light emitting diode arranged to be illuminated when "set" switch has been operated to start the timer.

6. An alarm system as claimed in any preceding claim, in which the alarm switch means, the timer and the set switch and associated circuitry are contained in a box and the "cancel" switch is remote from the box but is connected thereto by lead wires.

7. An alarm system as claimed in any preceding claim which incorporates its own audible alarm bell or siren.

8. An alarm system as claimed in any preceding claim, which has terminals for connection to a separate burglar alarm orto a remote alarm.

9. An alarm system as claimed in any preceding claim, which incorporates its own battery as its source of power.

10. An alarm system as claimed in any precding claim, which has an output relay with contacts connectibleto or connected to an internal or external alarm bell or siren and further contact connectible to or connected to a separate or remote alarm.

11. An alarm system as claimed in any preceding claim, which is provided with a voltage stabilizing capacitor to prevent a temporary drop in power voltage to the system upon connection of an inductive load.

12. An alarm system as claimed in any preceding claim, in which the timer comprises a capacitor, a discharging resistor connected thereto, a bistable circuit for initiating discharge of the capacitor when the bistable circuit is changed over, and a Schmidt trigger responsive to discharge of the capacitor, the "set" switch being arranged to change over the bistable circuit.

13. An alarm system as claimed in claim 12, in which the "cancel" switch is arranged to reset the bistable circuit and a diode is arranged to shortcircuit the discharging resistor and thereby recharge the capacitor when the bistable circuit is re-set.

14. An alarm system as claimed in claim 12 or 13, in which a reference voltage for the Schmidttrigger is applied through a normally-closed switch or series of remote normally-closed switches, such that opening of that switch or one of the series of switches sets off the alarm.

15. A personal alarm system constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.