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In-vehicle security systems, anti-theft causes the horn to sound and the lights to flash if someone tries to break into your vehicle. There are several different ways to trigger the alarm. Typically, the driver sets the alarm by operating a switch when leaving the car. Opening or forcing the hood, trunk, tailgate, or door to open also causes the alarm to trigger. Many vehicle security systems include a starter interruption, which prevents starting the engine after any forced entry. Some vehicles automatically disconnect electrical circuits to stop a car from starting or shut down the engine.