also i mostly see security room to be places where "metal detectors", CCTV and Guard hangouts if they aren't assigned or have nothing to do (not resting thats done in a staff room)
basically this is how i would want the arrivals to be handled.
- arrival (in criminal clothes)
- marched into "check in" room
- when a prisoner has been search, register and provided their overalls they are put in the holding cell
- when all new arrivals has been processed guards will then start allocating them to cells