Al, as far as I can tell, the main problem with tracking devices is the size. The smallest I've seen fits into the palm of a hand. They need (a) power to transmit a signal (b) a powered receiver to track the GPS location. All perfectly feasible for something as large as a car - not so feasible for a small or sensitively made musical instrument. By "sensitive" I mean an instrument where the addition of a plastic box affects the look and tone - such as a violin.

The problem is not so much with the chip as with the peripheral circuitry and power output required to make it work. The other problem is one of setting it off. When a car is broken into, a circuit can be activated - much as a car alarm is activated - which triggers the tracking device. No such triggering is available for an instrument as far as I know.

All this describes "active" tracking systems. I suppose 'passive" systems are more easily implemented - i.e. the equivalent of special "invisible" paint on a bicycle frame, or a chip in the neck of a dog - but they require some device to read the paint or chip. If I walk on stage carrying your expensive, stolen Jefferies concertina, who's going to have a chip scanner on their person to check my honesty?