There is a pearl glitch/mining detector above, and a mining detector below, the cell. Everyone respawns inside via a squilly bed glitch using a shulker. There is no specified way out since there are no guards. If the default spawn spot is filled with blocks, everyone spawns in a higher location where they are detected and an area ban is triggered.
More Security
There are a lot of trap portals and area bans all around the prison, and these are surrounded by wither walls. Below the prison there is another pearl glitch detector and above there is a mining down/pearl on top detector using pressure plates. In the visiting process everything is watched by observers.
