The Opus is connected to the battery for main power, to a 12v+ ACC/IGN for sensing ingnition and a ground. When you start your car, it senses the ACC/IGN and it sends a signal to the computer to boot up or come out of hibernation/standby just like you were pressing the PWR button. It boots up and runs. When you turn the car off it will no longer sense the ACC/IGN and send a signal to the computer to shut down/hibernate/standby. It's pretty slick. Go to opussolutions.com and read up on it and do a search here. There's tons of info on this subject. Hope this helps you out some.