You do realize that if you leave your car unlocked and some one hotwires and steals it some insurance policies won't cover that right? Also, if the door is unlocked it is no longer considered "breaking into" the car if they decide to steal something. Much like if you leave your front door unlocked and somebody enters your house. It is no longer "breaking and entering" because they didn't have to "break in". Besides that alot of criminals that will break into a car just to look won't even try the door to see if it is open.