I have an old Corvette and when I get out of the car I switch the coil wire in the distributor with a spark plug wire. This is very low tech but I have a feeling would do the job. The car just backfires when you try to start. Its hard to initially see what is wrong so hopefully they will just move on.

A friend of mine and I discussed various ways of screwing with car thieves a while ago, and we came up with a few non-standard methods that might be effective, such as these:

1) Put a non-return valve in each brake circuit, with an electrically operated via hidden switch bypass valve across each one. End result is when the brakes are used, they stay on, and the harder you press the worse the situation gets. Car immovable.

2) Put a pressure-switch (oil pressure type) in the brake circuit, and wire it to the horn. Every time the brakes are used the horn goes off. Car movable, but very obvious

3) mount a small scrolling led sign in the back window, and set it up so it normally acts and looks like a high-level brake-light. If the car is started without the hidden switch being disarmed, sign scrolls ''I am a stolen car''. Attracts police attention.

pca

Genius! All of them!