I've been in buildings were people enter an occupied floor during office hours, go into the stairwell (no card needed to exit through the stairwell), and prop t

I've been in buildings were people enter an occupied floor during office hours, go into the stairwell (no card needed to exit through the stairwell), and prop the door open with a brick or a piece of cardboard so it can be re-entered from the stairwell later. You'd think that would trigger an alarm and alert someone, but I guess not in every case. People walking by typically don't mess with a propped-open door, either, because they assume it's propped open for a reason.