I used to lock them inside back in college quite often. Studying, worrying, running late, etc. so I started carrying a spare and hid one as well. Now I'm out in the woods and places far from help often, so it would be REAL inconvenient to lock them in. Although I can't remember the last time it happened now.
That is funny. Since I started carrying the spare in my wallet, I may have used it once in the last 20 years.