In addition to the relay to the horn, tape a cherry bomb or an M-80 to a 1-Lb. can of cayenne pepper under the seat. With a little ingenuity, your horn relay can also power an electric ignitor for the M-80. Very few car thieves can keep their mind on their business with a faceful of red pepper!
I used a slight modification of this idea when cars stored at my high school automotive shop were getting vandalized. I took a 2-foot length of 1" PVC pipe and found a piece of broomstick that was a snug slip fit inside it. A piece cut from a truck innertube was duct-taped to the pipe, then the broomstick was pulled out until it gave the rubber a good stretch. I drilled a hole for a cotter pin to block the broomstick in the cocked position, filled the pipe with ground cayenne, painted everything flat black, and duct-taped the whole works to the steering wheel, aimed at the driver's door. A piece of monofilament fishing line from the door to the cotter pin completed the setup. It got tripped a few days later. One of my chronic troublemakers didn't come to school for 3 days, and when he returned, he had some very irritated-looking eyes, and a broomstick-sized bruise on his forehead! No more problems!
Jerry
