Many states have laws that define the operation of a vehicle as having the keys in the ignition. If you are planning on sleeping off a night of drinking in your car instead of driving (a seemingly good idea), make sure you don't put the keys in the ignition to turn on the radio or operate any other accessories or else you could get busted.

This actually happened to a friend of mine. He was sleeping in his car, with the keys in the ignition to listen to the radio. A couple rolled up and started hassling him, and took him in on a DUI. And he got convicted! He got the same sentence for sitting in hos car drunk listening to the radio as he would have gotten if he was driving down the road endanger people's lives.

So remember, if you are sleeping off a night of partying in your car, keep the keys out of the ignition.