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 from the driver of a non-immobilizer car.
Car alarms can be divided into two 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)
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
- Motion detector
- Wireless USB