The Problem:
Car theft is still very common in urban areas. While many car alarm systems use loud noise to draw attention, they can be overridden and are not much of a deterrent to those committing the thefts. Recovering stolen automobiles is a difficult task for law enforcement and their already busy schedules do not afford them much time or energy to put into these searches, so it would be most effective to stop the crimes from taking place in the first place.
Biomimicry Idea:
When disturbed by predators, garter snakes release a foul odor that makes them completely unappealing to their attackers. By creating a system that allows automobiles to release a disgusting, pungent smell when broken into, nauseated car thieves would be forced to rethink their decision to commit such crimes. It would be important to use a chemical compound that is strong enough to make humans feel ill, yet would not permanently stain the interior and spoil the driving experience for its rightful owner.