My father disconnected the distributor (correct word?) and took a piece of it with him. Definitely a killswitch. That was in the 70s. Cars got more complicated around 1980.
> My father disconnected the distributor (correct word?) and took a piece of it with him.
Yes, my dad was used to removing the rotor from the distributor (small piece, easy to pop off and unless the thief just happens to have the correct model handy, the car can't run) back in the 60s (maybe he did it earlier).
I'm pretty sure some form of this has been popular for just about as long cars have had an electrical system.