You need a powerful radio transmitter and at least two receivers in different locations to "triangulate" the location of the radio transmitter.
The transmitter uses a lot of power so its battery will be pretty big. The transmitter will need a radio station licence for you to use it.
This is for Shax. How do I go about buying one of these devices that you build? I s this still avalid site? I notice all the msgs are years old. I can't seem to get my msg posted. This is the 2d try. Let me know OK? Thanx. Scifiocean