Here is the thing, though... An unlocked door isn't a key left carelessly in the ignition. If someone was going to steal your car, I don't think a locked door would stop them. So either way your car is gone. And tbh, unless you live in a metropolitan area it is highly unlikely your car will be stolen. Most people who intend to steal your belongings inside your car will not piss on your seats either if they find nothing. Despite popular opinion, there are some fuck-ups that will damage other peoples belongings just for shits and giggles. I for one found out about this first hand -- broken sunroof, kicked in fender, broken taillight, smacked up bumper(this was a hit and run).