You know that your car alarm and keyless entry system turns your car alarm on and off, and locks and unlocks your car’s doors, but you’re not sure how. When you push the button to turn off (disarm) your car alarm and unlock the doors, the remote sends a signal to the control unit. The control unit then sends a signal to an electronic component known as a relay. A relay is a type of switch that can handle up to 30 or 40 Amps which is needed to lock and unlock the doors. This relay has a high current power and ground connected to it. With the signaling wire from the controller, and a high current output that is connected to the solenoid, this locks and unlocks your car’s door. Usually, there is one relay for lock and another for unlock.
For more info, see 4 Easy Step to Properly Perform a Car Alarm Installation