The cell is surrounded by detectors, but itself is very permitting. There is an end portal so prisoners can go to the end, and they can also go to the nether. When coming back from the end, prisoners will be trapped in a detecting, inventory banning death box which, once they die in it, will open another respawn point for a few seconds to let them respawn in the cell. The roof detector also functions as the top detector for the cell. Since it's made of glass, signs, and tripwires, the sky is visible through it. In the nether, there are also a lot of detectors surrounding the region in which the cell can generate a portal.
More Security
The prison is surrounded, in the overworld, by many submerged fox boxes which are themselves surrounded by some weak wither walls. If someone decides the wither walls are not worth their effort and attempts to wither above them, they will hit a budded piston wall that triggers the suicide on the inside.
