Are you 100% sure your car's central locking works? Mine doesn't.
 

My wife discovered today that you could open the rear driver side door even when my car was locked. Because it's all electric there are no individual door locks, so opening any door (from the inside) automatically unlocks the other three. In this case the culprit door doesn't appear to be locking at all, which means it can be opened from the outside regardless.

Result... if my car is locked and that one door is opened, all doors unlock and will remain unlocked.

For all I know it could have been like this since I acquired the car 4 1/2 years ago... hopefully it's just a bad connection or a dead relay/solenoid.

Check that your central locking works properly! Go right now!