Other thing that I forgot to mention!

Elevators will not open if there is a problem with the doors. This is a safety mechanism.

So, if there are pebbles in the door tracks (the little groves at the bottom where the doors slide), the doors may get stuck and, as a result, the elevator WILL NOT MOVE INTENTIONALLY.

(So that way no one is sandwiched between the doors when it moves, getting cut or hurt or squished or whatever other crap you see on TV.)