> If you want to lock the door, then the hidden control problem becomes evident... to lock the door, I must know that the hidden control to lock is the pound key. To make matters worse, it's not a simple press of the pound key. It's a press of the pound key for a full five seconds in order to activate the lock sequence. The combination of the long temporal window and the hidden control makes locking the door nearly impossible, unless you are well acquainted with the system and its operation.

Isn't that kind of the point? You don't want people accidentally locking the door, but if it's your door, it's easy enough to remember how to do it.