GB2158979A - Alarm equipment - Google Patents

Abstract

There is described a car alarm (8) having a visible or audible warning means which is actuated by external or internal interference with the car, e.g. resulting in vibration on a drop in the voltage of the car battery, wherein the alarm (8) is adapted to lock on to a steering wheel (10) of the car, preferably to prevent turning thereof. Additionally, there is disclosed alarm equipment comprising: an internal power source (3); means (5) for comparing a first voltage, derived from a power source (1) of apparatus in which, in use, the alarm is installed with a second voltage derived from the internal power source (3); and visible or audible warning means (2) which is actuated in response to a difference between the said voltages as detected by the comparing means (5). <IMAGE>

Description

SPECIFICATION Alarm equipment This invention relates to alarm equipment.

Alarms are well known, for example house or shop alarms and car alarms. Known alarms, however, suffer from the not inconsiderable disadvantage that they require installation by someone who has electrical and mechanical skills which are needed to fit the alarm to the object which is to be protected. This complexity renders the alarm system of the prior art expensive and consequently discourages many people from fitting such systems.

According to the present invention there is provided alarm equipment comprising: An internal power source; means for comparing a nrst voltage, derived from a power source of an apparatus in which, in use, the alarm is installed with a second voltage, derived from the internal power source; and visible or audible warning means which is actuated in response to a difference between the said voltages as detected by the comparing means.

Thus, with articles such as cars, caravans, mobile huts and the like, there is generally a power source by which various functions of those articles are operated. Taking the example of a car, the car battery provides power for the internal lights of the car as well as instantaneous power for the ignition of the engine of the car and power for operation of functions such as heaters, windscreen demisters and windscreen wipers. At the instant a function of the car is operated, the load on the battery causes its output voltage to drop for a short period of time. In accordance with an example of the invention, by providing a comparison circuit which compares the voltage of an internal power source of the alarm equipment with the voltage of the power source of the car, a variation in voltage may be detected upon actuation of functions of the car.For example, when a car door is opened, the courtesy light of the car is switched on and this will, as explained above, give rise to an instantaneous drop in voltage at the terminals of the battery which can be detected by the comparison circuit. The detection of a change in voltage can be used to operate a switch which actuates a visible or audible alarm of the alarm equipment which is, for example, driven by the internal power sorce of the alarm equipment.

Preferably, a delay system is provided such that the alarm is not actuated when, for example, a driver of the car leaves the car.

With regard to the application of alarm equipment according to the present invention to a car, the connection to the power source of the car may be made via a cigar lighter of the car. This provides a simple, but efficient, means by which the power source of the car can be accessed. Naturally, the action of removing the connection from the cigar lighter would result in the alarm being actuated.

In another aspect of the present invention, there is provided a car alarm having visible or audible warning means which is actuated by external or internal interference with the car, wherein the alarm is adapted to lock onto the steering wheel, preferably to prevent turning thereof.

The visible or audible warning means may be actuated by vibration of the car, in which case the trigger may be a vibration sensing or an ultra-sonic or a doppler switch. Alternatively, the warning means may be triggered as described for the alarm of the first aspect of the present invention.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: Figure 1 schematically illustrates alarm equipment according to the present invention and its connection to, for example, a car; Figure 2 illustrates on embodiment of an alarm in accordance with the second aspect of the present invention in engagement with a steering wheel of a car; Figure 3 illustrates the alarm shown in Fig.

2 in isolation from the steering wheel; Figure 4 illustrates another embodiment of an alarm in accordance with the second aspect of the present invention engaged with a rim of the steering wheel; Figure 5 and 6 show an alternative construction to those shown in Figures 2, 3 and 4; and Figure 7 is a circuit diagram of the equipment shown in Fig. 1.

With reference to Fig. 1, the alarm equipment has an internal battery 1 providing power to an audible alarm 2. The alarm equipment is connected to a battery 3 of a car. the battery 3 also supplying the power to the alarm 2. Provided that the two batteries 1, 3 maintain substantially matching voltages, the alarm 2 remains off. However, if the voltage of the car battery 3 drops, the alarm 2 will operate. This change in voltage of the battery may arise by virtue of a courtesy light being switched on, by the engine being started, or by another device in the car causing a current to be taken from the car battery 3. The alarm 2 will also operate if the car battery 3 is disconnected entirely from the alarm equipment.

The battery 1 of the alarm equipment provideds power to a switch 4 and, via switch 4, to the alarm 2. The battery 1 also provides a reference voltage to a comparator 5. The car battery 3 provides a sample voltage to the comparator 5. If the voltage from the car battery 3 drops below that of the battery 1, a signal is passed to the switch 4 via an optional delay 6 to actuate the alarm 2. The optional delay 6 is provided to enable an authorised person to switch off the equipment with switch 7 before the alarm 2 operates.

This delay 6 may be adjusted as desired.

The connection to the car battery is preferably made via a socket of the car, such as a cigar lighter.

With reference to Fig. 2, alarm equipment 8 is shown clamped to the rim 9 of a steering wheel 10. The equipment 8 in this position is switched and locked on, and may be removed as shown in Fig. 3, by an authorised person.

In Fig. 3 the alarm equipment is shown to comprise two portions, a first portion 11 and a second portion 12, the two portions veing connected by hinge 14 at one end of the two portions 11, 12. Each of the portions 11, 12 is provided with a groove 13, which on the closure of the alarm equipment, grip the rim of the steering wheel.

Alternatively, as shown in Fig. 4, the switch in the alarm equipment may be constituted by a lead 1 5 which is adapted to pass around the rim of the steering wheel 9 to make an electrical connection between two contacts in the alarm equipment. Breaking of the lead results in actuation of the warning means.

Fig. 5 and 6 show a further form of alarm equipment which may be locked around the rim of a sterring wheel. The equipment conprises a circular casing 1 6 with sound holes 17, the casing having a groove 1 8 in which the rim may be locked via a lock 1 8 having a locking tongue 1 9. The lock may be released by a key insertable into a key hole 20 An external connection to a cigar lighter of a car is provided by way of a cable 21 and a plug 22.

The equipment of Figs. 3, 4 and 5, 6 may be adapted to use circuitry according to Fig.

1, or alternatively this may include other means for causing an audible or visible alarm, such as a vibration sensing switch, an ultrasonic switch or a Doppler switch.

Fig. 7 is a circuit diagram of an embodiment of the circuitry of Fig. 1.

To switch the alarm equipment on, a switch 51 is closed, switch 52 being opened. A capacitor C1 charges up so that a transistor T1 starts to conduct to bias a transistor T2 off, allowing a transistor T3 to conduct when triggered, this normally being biased off by the car battery. if the car battery level drops, transistor T3 is turned on, a thyristor T4 fires, a capacitor C2 charges up, a transistor T5 conducts, a thyristor T6 fires and the alarm 2 sounds. The capacitor Cl provides the delay to give time to allow the owner to open switch S1 (and thereby close switch S2) and get out of the car before the alarm can sound.

Claims (6)

1. A car alarm having a visible or audible warning means which is actuated by external or internal interference with the car, wherein the alarm is adapted to lock on to the steering wheel, preferably to prevent turning thereof.

2. A car alarm according to Claim 1, comprising: an internal power source; means for comparing a first voltage, derived from a power source of the car in which, in use, the alarm is installed with a second voltage derived from the internal power source; and visible or audible warning means which is actuated in response to a difference between the said voltages as detected by the comparing means.

3. A car alarm according to Claim 2, which includes a plug adapted to be received by a cigar or cigarette lighter socket of the car for electrical connection of the car alarm with the car such that the first voltage may be sensed.

4. Alarm equipment comprising: an internal power source; means for comparing a first voltage, derived from a power source of the car in which, in use, the alarm is installed with a second voltage derived from the internal power source; and visible or aduible warning means which is actuated in response to a difference between the said voltages as detected by the comparing means.

5. A car alarm substantially as hereinbefore described with reference to, and as illustrated in Figs. 1 to 7 of the accompanying drawings.

6. Alarm equipment substantially as hereinbefore described with reference to, and as illustrated in, Fig. 1; and Fig. 7 of the accompanying drawings.