Curious about NS train door keys

So a few times I see the train workers/conductors (not sure) stand with these turning keys/dials at the door, turn it at the door key pad where the buttons are to open, look outside as I assume their colleagues are doing as well, then turning it or coming inside and turning it. What is this for? Something with the doors? Might be a really straightforward common sense thing but I come from a country with no trains so this a new thing for me to see!

Edit: *country with maybe 2 passenger trains total in cities 10 hours drive from me