I just remember back when I was visiting/"sightseeing" Shackspace, the hacker space in Stuttgart, Germany.

They had built a door lock whose bolt was driven by some microcontroller with a web interface. So they could give out permissions and open the door with their smartphones (important because very large and diverse set of people who want to enter – physical keys would have been impractical).

I was really surprised when there was a glitch and some guy couldn't open the door anymore. The door was bolted, and for a minute or two noone could enter or leave.

I think that was the most blatant (and scary) violation of just about every fire code in existence that I've ever experienced first hand.