Humane Restraint locking mental hospital restraints
I got these from my neighbor when he was the facility manager at a psychiatric hospital, they no longer use restraints on the patients apparently.
Here's an overall view:
These were used on the beds in the isolation rooms for unruly patients, here's a closer look at the wrist strap, note the locking post:
here's the lock, this hole is where the locking post fits:
here it is locked, note the locking piece in the hole, this would engage the slot on that post:
A look at the key, pretty simple:
Here's the side of the lock, there is a single pin in there that has to be raised by that key, allowing the locking piece to slide out: