Another function required to make PCs work in a car is start-up and shutdown control. Making a PC start with the car and shut down with the car requires special circuitry, which is often integrated with the power
supply. When the key is turned on in the car's "accessory" wire (IGN) provides 12V, which triggers the controller to "press" the power button on the PC. When the car turns off, that button is "pressed" again. Some units provide a delayed off, preventing shutdown during short stops. If the unruly PC fails to shut off, the shutdown controller will eventually cut power to the PC, ensuring that the battery of the car doesn't get drained.