The PockeTracker incorporates a TinyTrak PIC IC and a VHF Dual frequency 200 mW transmitter. It was a product of Byonics, but is no longer available for sale there.
PocketTracker has the option in the later model to change the frequency of the transmitter by talking directly to a divide by network.
In the previous model the frequency of operation was fixed between two different know frequencies.
The main advantage of the PocketTracker is its low power consumption. It can run for something like 100 hours on a 9Volt battery.