Car Alarms work by emitting high-volume sound (usually a siren, klaxon, pre-recorded verbal warning, the vehicle's own horn, or a combination thereof)  as well as by flashing some of the vehicle's lights, and (optionally) notifying the car's owner via a paging system and interrupting various electrical circuits necessary for the car to start.

Because of the large number of false alarms with car alarms, many vehicle manufacturers no longer factory fit noise-making alarms, instead they offer silent—but effective—immobilizers.

An Immobiliser or immobilizer is an electronic device fitted to an automobile which prevents the engine from running unless the correct key or code is presented.
This prevents the car from being "hot wired".

The first Satellite Navigation system was Transit, a system deployed by the US military in the 1960s.

A CD Changer holds multiple Compact Discs, usually in a cartridge, and allows the user to access any of them, one at a time.
External cartridge CD changers have one or more cartridges that the user loads with up to 12 different CDs and then inserts into the CD changer.
The CD changer can then remove one CD at a time for playing.
This type of player is commonly found in vehicles because the user can switch easily between large amounts of media contained in different cartridges.

For more information on car alarms take a look at Car Alarm Forum

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