I believe it should go without saying that all prisoners should be seatbelted for the ride from the point of arrest to the point of incarceration, both for the safety of the prisoner in the event of a collision, and the safety of the officer and the vehicle should the prisoner get froggy.
Here is a tip to increase the restriction of movement of a prisoner:
Most factory installed seatbelts are equipped with a ratcheting system to secure child seats. The ratcheting mechanism is engaged by pulling the seatbelt all the way out, then letting it retract. If the ratcheting mechanism is engaged, you will here a continual clicking as the seatbelt retracts and you won’t be able to pull it back out unless you retract it all the way to its resting position.
First, put the seatbelt on the prisoner and pull the shoulder belt to tighten the lap belt.
Next, pull the shoulder belt all the way out from its retractor until it stops.
Then allow the shoulder belt to feed back into the retractor until it is snug against the prisoner.
To check and see if you have effectively secured the belt in its ratcheting mode, attempt to pull it out from the retractor. It should be solidly locked and not pull out. This should help to limit the movement of your prisoner. When you take the seatbelt off your prisoner and it retracts completely, it will return to its normal operation.
If your cruiser still has an owner’s manual in the glove box (I know...fat chance), you can look up the seatbelt function in there.
Be safe.