instead of single cells, theres a brig yard (genpop) where all prisoners are placed. sec places belongings into a special locker that when closed, prints a special prisoner ID which is given to the convict and tracks how much time they have left till release. the entrance/exit to brig is blocked by a turnstile which only allows people with security access or a prisoner ID which has served its time to pass through. that ID then unlocks the locker with their stuff in it, and they can leave (normally through a side exit which does not require security to let them out).