This is a car alarm simulator which using the LED as a simulation output. This simple circuit can tell you whether your car is running or not by detecting the voltage difference when the car is on and off. This occurs because when your car is running the Alternator puts a out a voltage a little bit higher than when the car is off. This circuit act
ually is a kits, you can get the kits at But it is very possible to you to build your own car alarm simulator circuit.