A Lojack system is an electronic tracking system that is usually used to locate a vehicle that has been stolen. With the increased frequency of vehicle theft, the use of the Lojack system is on the increase. The Lojack system is installed in a hidden place in the vehicle. The way the system works is, when the vehicle is reported stolen, a radio signal is sent out to the Lojack device hidden in the vehicle. This radio signal is sent from a computer activation by the police. After activation, the police are able to track the whereabouts of the vehicle.
For more info, see What is an Anti-Carjack System?