Going to a call where you might come out with a prisoner? Think ahead...
I got this one from my father-in-law, San Leandro (CA) PD Officer Dan Ruff:
Unlock your doors, then prior to exiting your vehicle, manually press down the passenger’s side front door lock and your driver’s side front door lock as you get out. That way, when you get back with your prisoner, your front doors are both locked but your back seat is unlocked so you don’t have to fumble with your keys while holding on to your prisoner.
Now, no one can get into your vehicle, that is unless they want to get in your back seat.