Microsoft installed their Xbox motion-detecting camera, the Kinect, in the ceiling above the elevator, then had it monitor people for months, determining what behavior predicted whether they'd board the elevator or not. If the camera determined someone was likely to be getting on, the doors opened, which, yeah, sort of creepy. But it also does this cute thing where if it isn't sure whether someone is going to get on, it'll jiggle its doors until the person motions to tell it to wait or not. Have you ever held the door for someone because you thought they were coming on and then they wave to say No, thank you, I'm not getting on, and you're worried afterwards that everyone on the elevator is burning with fury because you made them wait needlessly? That's what this does, essentially. Progress.