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What is the alarm/what does it do?

An alarm is an electronic alarm fitted in a car, which is part of the car's safety and security system, designed to deter would be thieves from stealing the car, or any belongings kept within the car. A car alarm is, therefore, a useful piece of kit in providing some peace of mind when leaving your car parked unattended. Car alarms are often fitted into the car by the manufacturers at the time they are manufactured but there are also aftermarket alarms available, which can be fitted after the car has been built. 

Getting into the details of the alarm

A car alarm works by producing a very loud, often piercing, noise which is designed to stop the would be thief, which is triggered by certain factors. Sometimes the sound produced will be a siren or maybe the car horn will sound constantly or in some cases a pre-recorded voice gives out an alert message. In some alarm systems the lights will flash on your car as an extra alert. Advanced car alarms will be programmed to send a message via text or pager to alert the car owner that the alarm has been activated. Certain alarms will shut down the electrics on the car when the alarm is sounded, therefore immobilizing the vehicle, so that it can't be accessed or started. What actually sets the alarm off will depend on the make and model of the alarm. Aftermarket alarms are usually universal, meaning they are made to work with all makes and models of car, but can be adjusted or configured to individual requirements which means the driver can choose to activate certain alarm triggers and disarm other triggers if they wish. 

Most alarms have an electronic sensor, known as a shock sensor, and a control unit, which connects to the battery of the car. When the alarm is activated, it can be set off by a vibration picked up by the shock sensor; a change in voltage caused by a door being opened; or the ignition being turned on, for instance, which the alarm recognises as an intrusion. Some alarms will have the option to add extra sensors if desired, such as a specific sensor which is triggered by the sound of glass breaking; motion or proximity sensors which detect movement in or outside the car; or a tilt sensor which recognises when the car is being towed away. One such specififc sensor is the anti pinch sensor; an important safety feature of the car alarm system. Used in cars with electric windows, its function is to detect when something obstructs the window or someone tries to break into the car through the window. The anti pinch sensor is situated in the seal around the window and is specifically set to detect when an obstruction or intrusion happens in the space between the edge and frame of the window. 

Part of the car's safety system, often working in conjuction with the alarm, are the locks on the doors. Some complete vehicle lock sets operate with a remote keyless central locking system which means by  pressing a button on a remote control the locks included in the set will lock or unlock and this can also activate or deactivate the alarm system on the vehicle.

What if something goes wrong with the alarm?

If the alarm on your car is not working properly and keeps sounding when it shouldn't, it could be that the settings on the sensors need to be adjusted.  It could, however, mean that the alarm has not been fitted properly or is faulty and will need to be replaced.