Car alarms should not be confused with immobilizers; although the purpose of both may be to deter car theft, they operate in a dissimilar fashion. An immobilizer generally will not offer any audible or visual theft deterrence, nor require any additional input from the driver than the driver of a non-immobilizer car.
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Car alarms should not be confused with immobilizers; although the purpose of both may be to deter car theft, they operate in a dissimilar fashion. An immobilizer generally will not offer any audible or visual theft deterrence, nor require any additional input from the driver than the driver of a non-immobilizer car.
Car alarms can be divided into 2 categories:
- OEM (built-in to the vehicle at the factory)
- Aftermarket (installed at any time after the car has been built, such as by the new car dealer, an auto accessories store, or the vehicle's owner)
e alarms come with a mix of features. Remote car alarms typically consist of an additional radio receiver that allows the owner to wirelessly control the alarm from a key fob. Remote car alarms typically come equipped with an array of sensors along with immobilizers and motion detectors.
Keyless remote car alarms are typically based on strong cryptography authentication methods.
- Radio receiver
- Immobilizer
- Motion detector
- Wireless USB
OEM alarms
Almost all OEM alarms are typically armed and disarmed with the vehicle's keyless entry remote. On many vehicles the key cylinders in the driver or front passenger door activate switches, so that when a key is used in the door the alarm will arm or disarm. Some vehicles will arm when the power door lock switch is pressed with the driver's door open, and the door is subsequently closed. Some vehicles will disarm if the ignition is turned on; often when the vehicle is equipped with a key-based immobilizer and an alarm, the combination of the valid key code and the ignition disarms the system.
Aftermarket alarms
Like OEM alarms, aftermarket systems are usually armed and disarmed via remote. Usually they do not have provisions for external disarming from the key cylinder, but will typically have an override switch mounted in a hidden location.
What sets an alarm off?
The individual triggers for a car alarm vary widely, depending on the make and model of the vehicle, and the brand and model of the alarm itself (for aftermarket alarms). Since aftermarket alarms are designed to be universal (i.e., compatible with all 12 volt negative ground electrical systems as opposed to one carmaker's vehicles), these commonly have trigger inputs that the installer/vehicle owner chooses not to connect, which additionally determines what will set the alarm off.
OEM alarm triggers
Generally, OEM alarms monitor the doors and trunk/hatch for unauthorized entry. On some vehicles this is done through pin switches, mercury switches, or microswitches integrated into the latch. On others, the doorlock mechanisms have switches built into them. Some OEM alarms additionally will trigger if the hood is opened, or if the ignition is turned on. Additionally a few systems have a shock sensor which will trigger upon a significant impact to the vehicle's body.
