Jersey City has car alarms and security systems for sale. A car alarm, in its simplest form, is an alerting system whereby the owner is made aware of a theft attempt by emitting a sharp siren when someone forces their way into the car. Many less and more sophisticated variations of the alarm are now available. Many cars come equipped with a Original Equipment Manufacturer (OEM) car alarms nowadays, or one can get them installed by contacting the auto manufacturer. The aftermarket car alarms are usually more sophisticated and have many features. A modern car alarm comprises a sensor array, a siren, a radio reciever to control the car from a distance (by the owner), an auxiliary battery to ensure that the alarm works even if the main battery is disconnected, and a computer control unit.