Military ships search for the RF radio noise coming from unknown ships. You would think you could do the same with a police car. I think there are two ways to do it. First would be to use a spectrum analyzer near a police car and see if it leaks a unique set of radio noise. If they do you could build something listening for that pattern. The other method would be to do as the VG2 does to detect radar detectors, listen for the osolator noise from their electronics. Like maybe listen for a lojack receiver and a motorola radio??
Anyone think this is feasable?