HOW CAR ALARMS WORK
1 Basic alarm layout
A range of different sensor types gives a greater range of information to reduce false alarms. Each relays information to the control unit, which is then able to ascertain whether the car is being subject to unwanted intrusion. Radar technology can also be used to deter thieves from even getting near to the car, by activating a warning ‘blip’ on the alarm.
2 Mercury switch
Mercury switches used to be used, on some older vehicles, to operate brake lights, which was a useful feature because the lights would be activated even when using gears to slow down. However, they have also a place within car alarm systems and can help to detect anything from a person entering a vehicle, to the slightest vehicle movement.
3 Motion sensor
The basic, but clever ‘shock’ or motion sensor uses nothing more technical than a metal ball in contact with a central ‘pole’ and a number of fanned-out base contacts. If the ball is only slightly disturbed, such as by wind deflection from a passing vehicle, the control unit won’t activate the alarm, but more pronounced agitation will set it off.