Car alarm system
Alarm systems in motor vehicles are intended to make the theft of a vehicle or components and objects that are in it more difficult by means of acoustic and visual alarms. Depending on the design of the system, all doors, the bonnet, the tailgate, vehicle movements, the interior as well as manipulation of the battery, the horn and the ignition can be monitored with various sensors. In the event of unauthorized access attempts, the horn and / or the lighting system (headlights, flashing lights) of the vehicle will be activated with regular horn tones and / or the headlight flasher to draw attention to unauthorized access. In addition, the immobilizer is switched on in appropriately equipped vehicles .
Such systems are regularly activated by locking the vehicle ( central locking ). Deactivation by entering a code or an external transponder is also possible.
Such warning systems are regulated differently around the world, so the acoustic alarm in the USA must not exceed four minutes. In Germany the signal horn emits an intermittent signal (approx. 2 Hz) for 25 to 30 seconds, in Switzerland it emits a continuous tone. The visual alarm occurs for five minutes via the hazard warning lights or for 25 to 30 seconds via the low beam.
In addition, there are now systems that alert the owner of the vehicle via SMS or e-mail and can display the vehicle's location determined via GPS to the rightful owner or an alarm tracking service provider.
criticism
Car alarm systems have long been the subject of criticism. Hardly anyone calls the police anymore because they are used to them. If the police are called, it is because of the noise caused by the alarm system. Most of the time, the alarm system is not triggered by a break-in, but by wind or vibrations.
Sensors
- Door contact switches - recognize the opening of the door and trigger an alarm after a few seconds
- Bonnet switch
- Door lock cylinder switches - are used to switch the alarm system on and off using the car key
- Radio - the alarm system detects that the cable on the radio housing is pulled
- Trunk lock switch
- Infrared, ultrasonic wireless interior sensors - monitor the interior and detect movements and the breaking of windows
- Inclination sensor or position sensor - detects changes in the vehicle's position and prevents theft by towing
Some alarm systems can also read out the CAN bus and evaluate its data.
For convertibles focused ultrasound systems have not proven as they have responded with open parked vehicles on any movement in the vicinity. However, microwave-based radar sensors are also well suited for use in a convertible, since only a certain field is monitored. This happens regardless of a spatial limitation, such as B. a hood.
Immobilizer
When the alarm is triggered, terminal 50 on the starter is interrupted via a relay . This means that the engine cannot be started. In addition, the fuel supply can be interrupted when the control units are networked with the injection system.
Individual evidence
- ↑ Matthias Breitinger, Why car alarm systems do not work - except Trouble Zeit-Online