Sniffing out stolen cars

If your car gets stolen an on-board system will immediately begin releasing a uniquely scented dribble from a hidden tank on it's underside. This can then be traced using a techno nose [link] mounted on the front of a robotic, self steering vehicle. The techno nose (protected from the elements by a large, rubber, nose-shaped hood and assisted in it's job by two fans sucking scent into the nostril shaped inlets) will be connected to the steering system of the robot. As the scent weakens and strengthens the techno nose wanders about following the strongest trace, and so sniffs out your car.