Vector technologies AA-2 Keeper

A beacon is surgically implanted under the victim's skin. It can only be removed by the being in possession of the tracker unit, who must first enter a password. Any other attempt to extract the beacon results in the release of an exotic neurotoxin that kills instantly (8D damage). The tracker can tell the range, direction, and speed of the target, up to a range of 25 kilometers. There's no need to worry about the target after that, because if he or she moves beyond that range, the beacon releases the neurotoxin automatically.