The DW unlocked the door to our 5er, inadvertantly turned the key back to the lock position, removed the key, went back inside for something she had forgotten, layed the key down, came back out, and closed the door. Oops! Only key is now locked inside.
Fortunately our basement door was not locked, and we have a clothes hamper under a trap door in the bedroom. So I clean out the basement, crawl inside, push up the trap door, push the basket up into the bedroom, and crawl up thru the small opening to the inside. Not the easiest thing for a 6'-5" person to do.
Now I keep two extra sets of keys in the truck.