Car alarms are electronic devices installed in vehicles in an attempt to prevent theft of the vehicle itself, its contents, or both. Car alarms work by emitting high-volume sounds (often in the form of vehicle-mounted sirens, honking, pre-recorded oral warning, vehicle's own horns, or a combination of both) when the conditions required for triggering are met. Such an alarm can also cause the vehicle headlights to turn on, may alert the owner of the car about the incident through the paging system, and may interfere with one or more electrical circuits required to start the car. Although cheap to obtain and install, the effectiveness of such devices in preventing vehicle theft or theft when their only effect is to emit sound seems to be negligible.
Video Car alarm
History
Early versions of car alarms for use as a theft prevention tool were discovered by unknown detainees from Denver in 1913. This version was armed manually, and was triggered when someone tried to start the engine. The alarm was later inspired by an early version of the remote starter published in 1916. This version has the owner of the car carrying the receiver, which will buzz if the car's ignition system is damaged.
Maps Car alarm
Features
Car alarms should not be confused with immobilizers; although both goals may be to prevent car theft, they operate in different modes. An immobilizer will generally not offer audible or visual theft deterrence, nor does it require more input from the driver than from a non-immobilizer car driver.
Car alarms can be divided into two categories:
- OEM (built in vehicle at factory)
- Aftermarket (installed any time after the car is built, such as by a new car dealer, car accessories store, or vehicle owner)
Alarms often come with various features. The remote car alarm usually consists of an additional radio receiver that allows the owner to wirelessly control the alarm from the fob key. Remote car alarms are usually equipped with various sensors along with immobilizer and motion detectors.
Car keyless remoteless alarms are usually based on strong cryptographic authentication methods:
- Radio receiver
- Immobilizer
- Motion detector
- Wireless USB
Arming and disarming car alarm
Remote
Usually car alarms are disarmed or armed by remote. Remote recently used scrolling code.
OEM Alarm
Almost all OEM alarms are usually armed and stripped away with keyless remote locks of vehicles. In many vehicles, the key cylinders in the rider or the front passenger door activate the switch, so when the lock is used in the door, the alarm will sound or disarm. Some vehicles will arm when the electric door lock switch is pressed with the driver's door open, and the door is then closed. Some vehicles will disarm if the ignition is turned on; often when the vehicle is equipped with a key-based immobilizer and alarm, a combination of valid key codes and ignition locks that disarm the system.
Alarm aftermarket
As with any OEM alarm, the aftermarket system is usually armed and stripped via remote. Usually they do not have provisions for external disarmament of the lock cylinder, but will usually have override switches installed in hidden locations.
Triggers
Individual triggers for car alarms vary widely, depending on vehicle brand and model, as well as the brand and model of the alarm itself (for aftermarket alarms). Since the aftermarket alarm is designed to be universal (that is, compatible with all 12-volt negative ground electric systems as opposed to one car manufacturer), this usually has unwanted trigger input by the installer/vehicle owner to connect, which also determines what will turn off the alarm.
Generally, OEM alarms monitor doors and trunk/hatch for unauthorized entries. In some vehicles this is done through pin switches, mercury switches, or microswitches that are integrated into the latch. On the other hand, the doorlock mechanism has a switch built in it. Some OEM alarms will also trigger if the hood is opened, or if the ignition is turned on. Some systems have shock sensors that will trigger significant impacts on the body of the vehicle, such as broken window glass. Motion sensors that monitor vehicle interiors are installed in some higher end models.
The simplest aftermarket alarm is a one part unit with siren and control modules. The most common types of sensors are shock sensors and two cables (constant 12 volt power and ground) connected to the car battery. This type of alarm is triggered by vibrations transferred to the shock sensor, or by a change of voltage on the input (the alarm assumes that a sudden voltage change is due to the door or trunk being opened, or the ignition key turned on); but is particularly vulnerable to false triggers in late model vehicles with many electronic control modules, which can draw currents with dead ignition.
More advanced aftermarket alarms are paired into individual vehicle electronics. Typically, these alarms have inputs for power and ground, as well as for positive and negative door open circuits, negative trunk circuits and/or hoods, and circuits enabled to detect the ignition switch; aftermarket alarms also usually have a shock sensor that can be built into the control module or externally for it.
In addition, some aftermarket alarms have provisions for optional sensors (these must be purchased separately). The tilt sensor can feel the vehicle tilted (warns to pull). The tilt sensor comes in digital or mercury form. The digital sensor is more accurate because it regulates itself, allowing the vehicle to be placed on a hill and not causing a false trigger. A discriminator of sound or glass destructive sensors only feels the sound of broken glass. Typically, the sound discriminator sensor can be removed using a shock sensor. Proximity sensor, infrared, or motion sensing movement inside or outside the vehicle; this is usually installed on a convertible or T-top vehicle. These sensors can usually be adjusted to avoid false alarms. For example, the shock sensor will occasionally vibrate due to the loud noise in the area, or the accidental impact of a car from a pedestrian. Proximity sensors can cause false alarms in the parking lot when a pedestrian enters or exits a parked vehicle next to an armed car. This often causes the wrong alarm to detect a piercing attempt.
Effectiveness
Although car alarms of some sort have been available since the beginning of the automobile era, a dramatic increase in their installations in the 1980s and 1990s coupled with the fact that almost all car alarms are triggered by accident (often due to high sensitivity settings) means that people who hear it often ignore it. In 1994, the New York City Police Department declared that car alarms could actually make crime problems worse, and there was one account in 1992 about a thief in New York City rocking a car to deliberately trigger an alarm to help hide the sound of broken windows.
Due to the many false alarms with car alarms, many vehicle manufacturers no longer use alarms that make factory noise, but offer silent immobilizers. Alternatively, an aftermarket vehicle tracking system may allow the police to track a stolen vehicle. Most police tracking systems require users to pay recurring fees, while factory immobilizers are included in the purchase price of the vehicle. GPS locating systems allow vehicle owners to lock and unlock, track, and deactivate vehicle starters online.
Frequently, false alarms occur because the owner of the car alarm uses a high sensitivity setting. This may be the main reason why the loud bass frequencies (hard music, cars or other motorcycles with a hard exhaust system, thunderstorms, etc.) can trigger a car alarm. The second possible reason is that some parts of the alarm system may not be installed properly.
References
See also
- Anti-piracy system
- Car searchers
- Immobilizer
- Long Range Acoustic Device
- Sound pollution
- Vehicle tracking system
External links
Source of the article : Wikipedia
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