It turns on when your car is on, off when it is off. Different ways to hardwire it and if you do that, you can record even when the car is parked. It records in 1, 3 or 5 minute intervals (some overlap 1 second, most will continue right where it drops off). It will then delete the oldest file so you can keep recording. 8GB gets you around 1hr of 1080p recording, 16 is 2hrs and 32 is 4hrs. Some have GPS to track your speed and location (some don't like it, some do).