Car alarm
From Wikipedia, the free encyclopedia
A car alarm is an electronic device installed in a vehicle in an attempt to discourage theft. Car alarms work by emitting high-volume sound (usually a siren, klaxon, pre-recorded verbal warning, the vehicle's own horn, or a combination thereof) when triggered or when circuit is breached.
Car alarms can be designed to be triggered by vibrations, tilting of the car (to prevent unauthorized towing), touching the car, the opening or closing of special switches (e.g. door contacts), sensing small but rapid changes in battery voltage (which might indicate an interior light going on, or the ignition circuit being activated), or using volumetric sensors such as ultrasound , infrared or microwave.
The vast majority of car alarms which sound are accidental. They are caused by the passing of large trucks, the vibration of thunder or people coming into contact with the vehicle.
Since most car alarms are triggered accidentally, most people in American cities are numbed to the sound of alarms, and do nothing to prevent theft. The New York City Police Department claims that car alarms are actually making the crime problem worse (see their booklet called "Police Strategy No. 5: Reclaiming the Public Spaces of New York," City of New York, New York, 1994) because since nothing is done about the alarms, the general impression is that no one cares about the neighborhood.
Because of the large number of false alarms with car alarms, many vehicle manufacturers no longer factory fit simple noise-making alarms, instead offering silent—but effective—immobilizers. Alternatively, an aftermarket vehicle tracking system can enable the police to trace stolen vehicles. Most tracking systems require the user to pay a recurring fee, whereas factory immobilizers are included in the purchase price of the vehicle. Both classes of devices deter someone from taking the vehicle without consent but do not cover theft from, or vandalism of, the vehicle.
Yet another class of security covers aftermarket car alarms that include 2-way paging controllers. Two-way pagers have remote control functions built-in, allowing the user to arm and disarm the alarm while informing the user of threats made to the vehicle. Some 2-way systems have an LCD icon display that can pinpoint the actual part of the vehicle being threatened. Many two-way pagers can also alert the user with beeps or silent vibration.
[edit] In popular culture
In modern times, it is frequent for car alarms to be used in movies or TV shows to add elements of comedy or drama to a particular scene, such as a character accidentally triggering one and being startled by the resulting noise, or having one set off when a catastrophic event happens to the car and/or in the immediate vicinity.
