Restraints

Iron slave collars along with manacles connected to iron belts by a short length of chain. This leaves the prisoners restrained, but doesn't affect their movement or speed.
Slipping out of the manacles OR collar require a successful DC20 Dexterity check, while breaking them requires a successful DC20 Strength check. A character can unlock them using thieves' tools with a successful DC 15 Dexterity check.