Since nobody here has claimed to be an elevator or escalator repairman, I think lots of you are talking through your hat (it may be a Borsalino, but it’s still not edifying). That said, I’ve been on lots of non-Shabbos elevators that have what’s apparently called a door safety edge, which is a mechanical switch. With such a safety device, there’s no infrared motion sensor.
I’m not an elevator repairperson but I’ll still chime in on the door safety features. Most modern elevators include all if the following.
1) A proximity sensor to prevent the door from closing if someone is approaching.
2) A light beam (or more likely 2) across the doorway to prevent to door from closing if someone is in the doorway.
3) A switch on the door edge will reopen the door if it hits an object while closing.
4) If there is too much load on the door motor it will reopen.
To the best of my knowledge, the first features is disabled on Shabbos elevators and the second may be partially of fully disabled. The final 2 will still work. I have not had the opportunity to test them.
My expertise with elevators does not include Shabbos elevators.