An Excerpt from the BMW Bible

Owner's Manual, page 27: Your BMW is equipped with a double-lock anti-lockout system. When the driver's door is open, its safety catch button can neither be pressed in nor the lock turned by the key. It is not possible to lock the vehicle using the lock button when the driver's door is open. This is a safeguard against locking yourself out of the car accidentally. Except of course at 6:45 A.M. on a Saturday morning when you pull up to the front gate at work, exit the vehicle to manually push open the broken gate, and return to your car (which is still running), only to find that the driver's door (with the handle that doesn't work from the outside) has closed, all other doors are locked, and your spare key is visible sitting in the cup holder. In which case, you are S.O.L. and must wait 45 minutes (with your locked car still running and sitting at the gate) for the locksmith to show up, pay fifty dollars for roughly 7 seconds of work, and be ridiculed by said locksmith for locking your spare key in the fancy BMW with the busted driver's door handle.