So, at work, we have this really cool pair of doors. Our office has big conventional locking wooden doors that lead into the lobby with the secretary. Behind the secretary is a pair of plexiglass doors. These doors are absolutely transparent, with metal pull-handles screwed through them, and a metal strip across the top and across the bottom. On the other side of the doors, at the top, are giant electromagnets. Magnets engaged, door won’t budge, magnets disengaged, door opens freely. No buzzzzzz or ca-chunk as solenoids engage. Simple silent locking and unlocking.
Now, these doors have a little digital keychain reader on the outside. Wave your keys across the pad, and they unlock for a few seconds–like Mobile Speedpass. The inside of the doors have a motion detector. Walk up to the doors, and they unlock.
Now, imagine work men coming in to mess with the security system. Suddenly the doors can still open from the outside, but the motion detector on the inside no longer works. From the inside, there is no way to disengage the electromagnets. There is no way to open the door. The Human Motel. Humans get in, but they can’t get out.
Soooo…. someone has to go out the fire door, walk down three flights of stairs, go around to the elevators, take those up to the third floor, and use the magic keychain to open the door. Niftiness.