When I was a penniless student, I had a very similar set-up to protect my ~18 y.o. car from joy riders, but the bottom of the chain went around the brake pedal. (Big problem where I lived because my digs where at the end of a long bridge that lead from the nightclub district through to a more residential area. People who drank all their cab money and tried to walk home would get off the bridge and be thinking “damn it’s a long way to walk” just as they got to my place.)

Anyway, the secret sauce on my version was that one link of the chain was twisted so that it pushed, with not quite enough pressure, onto the horn button. Any attempt to cut the wheel, cut the chain, or generally mess about with it in any way, would sound the horn (and quite tricky to twist it back out of the way to stop it.) I caught two thieves this way (both of ‘em juveniles.)