Radio collars broadcast radio waves of a specific frequency at a variabel rate. A directional antenna and receiver are used to pick up the signal. This equipment depending on make and model can either be hand held even mounted on a plane. A very accurate location of the collared animal can then be determined a field triangulation method which requires the use of GPS locates, compass directions and maps. It's the same way the FCC finds pirates!
There are three ways to track a tagged animal:
1. Radio collars are the least expensive, but are the most laborous to use as manual scanning is needed to finnd the missing animal. This may require a place to narrow area and then on foot to be precise. Radio tracking also requires telemetry equipment to pick up the radio waves emitted by the collar. but for only $900 you too can track your own household pets by radio!
2. Satellite collars are the most expensive, but require no monitoring in the field. The collar sends out a transmission which bounces off a satellite and back to a ground station. The location coordinates are then E-mailed to the research biologist.
3. GPS collars collect data continually. This data is stored in the collar itself. At the end of the tracking project, the collar disengages and drops off. the collar is colelcted and it's data uploaded to a computer. Both satellite and GPS collars have the advantage of being able to track animals over large distances, but not all locations. See map. Only $300 and a monthy service fee to track your pets by GPS!
What I'm not telling you so far is that the same technology is in your cell phone and you too are being tracked everwhere you go.