Any police cruiser with a tracking device will hear the signal from a distance of 5 to 7 miles, depending on the terrain. The device points to the signal's direction. The system became operational in Massachusetts in 1986. A unit costs $595 and entitles the buyer to a 20 percent discount on insurance. Through April 1988, stolen vehicles equipped with LoJack units have been recovered in an average of 90 minutes. When information about a stolen vehicle is entered into the State computer database, it automatically checks the information on vehicles equipped with LoJack. The database is updated daily. Tracking vehicles through the computer system greatly reduces the potential for a high-speed chase, because the thief is unaware that the police are tracking the vehicle. About 300 police cruisers are equipped with LoJack cruisers, at a cost of $1,500 each. Florida is the second State to adopt the LoJack system, and California will probably acquire the system as well. Photographs.