The tracking devices come in various designs. Each device works on a radio band and a three digit frequency which is separated by five megahertz. The pulse from the tracking device can be picked up from a high point using the directional or roof mount aerial to give the initial direction of travel.
The key-ring device is similar to the pendant in shape and colour except it has a small loop at the top which allows it to be attached to house keys, belt loops or pinned to clothing.
The wrist device has an internal aerial.