What do you mean by "bicycle defense system"? In downtown Chicago I've seen more than one bicyclist hurl a massive bike lock at a car which was acting aggressiv

What do you mean by "bicycle defense system"? In downtown Chicago I've seen more than one bicyclist hurl a massive bike lock at a car which was acting aggressive (following within inches of the bicyclist and leaning on the horn) but I doubt that's what you had in mind...