NEWS | Technology | Schoolboys create mobile seeker) reports some students from NZ developing a cheap mobile tracking device , which they call CellTrac-r (see pic). This was developed as a part of Business competition for pupils.
The detector seems to work by picking up bursts of radio frequency activity that mobiles emit each time it receives a call or text message. They have already sold 20 units (each priced at NZ$ 39.99 - around £15) and already have a name, StopCom, and a business model for it.
Young minds at their best !