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| Car Alarm Basics |
 A car alarm is an electronic device installed in an automobile with the aim to prevent theft. Car alarms emit high-volume sound (usually a siren, klaxon, pre-recorded verbal warning, the vehicle's own horn, or a combination of these sounds) in case if the car is triggered or when circuit is breached.
There are types of car alarms that are triggered by vibrations, car tilting (to prevent unpermitted towing), the opening or closing of special switches, touching the car, sensing small but rapid changes in battery voltage or using ultrasound or infrared sensors.
Most car alarm sounds are accidental. They result from large trucks passing, the thunder vibration or people coming into contact with the automobile. Because of that most American people don’t react to its sounds, and do nothing to prevent theft. The New York City Police Department claims that car alarms are actually making the crime problem worse because since nothing is done about the alarms, the general impression is that no one cares about the neighborhood.
The large number of false alarms forced manufacturers to stop producing simple noise-making alarms. Instead they offer silent but effective immobilizers. On the other hand, aftermarket vehicle tracking systems allow the police to trace stolen cars. Most such systems require the customer to pay a regular fee, while the immobilizers are included in the price of the car. Both types of devices discourage someone from taking the car without permission.
Another class car alarms include 2-way paging controllers. These pagers have built-in remote control functions that allow the owner of the car to arm and disarm the alarm while informing him of threats made to it. Some of these mechanisms have an LCD icon display that can point out the actual part of the car that is being threatened. A lot of such two-way pagers can also alert the user with special sounds or vibration.
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