Record a message played on a loudspeaker mounted under your car that starts with a demented laugh and then has a voice that says "Im coming to f*** you." Then have it go back to laughter. Have another speaker start playing the sound of a woman screaming. Just as that starts, your air horns start blaring and a blue rotating cop light starts flashing. Bonus points if you have a red strobe light in the car that starts flashing with no fixed interval. Have the brain hidden behind the passenger airbag or instrument panel, and have one that sends a remote message warning you that your car is being messed with. Maybe a couple of those handheld piezo sirens that you pull the chord on to activate. As you approach the car pull the chords and throw the sirens in a couple of directions (before they see you). I would only approach the car if it was one thief, he didnt see me, and I had a gun I knew how to use. Attacking with pepper spray is too risky, and more than one thief what if they both have guns?
Anyways, great advice on this thread!
It seems to me the most effective way is to bring fear into the equation- fear of getting caught, fear of the sick angry owner who just so happens to likely be a sadist, etc. A veteran car thief is pretty much immune to this- best way to avoid him stealing your equipment is to have a plane jane car with no stickers and as stealth an install as you can manage.
