it needs to be powered, there are some solutions that have an internal battery which can go into a sleep mode and can wake on impact and record, they're flawed in a number of ways, an internal battery is not a great idea but they also wake after the event and while if you're lucky you could catch some details of some offending vehicle or person involved you won,t have any proof of the actual event that triggered the camera to wake up
so what do people use overnight?