According to the article above, my suspicion that an implantable device the size of a grain of rice could be used to track someone via GPS satellite being total BS and bad fiction is correct. Seeing as how my Uncle was one of the first engineers to develop the implantable RFID chip for pets, I think I've learned enough about how they work to know they can't possibly even transmit a signal without an external source. It is the size of a grain of rice, how big could the battery be? If it even had one, it would be the size of a grain of sand! And that's enough to send a signal to a Satellite?! Yah freaking right.
Even a tracking device the size of a digital watch would only have a range of a few feet. Those tiny ear bud radios I see on movies can't have much of a signal range either, and a very tiny battery. So even if the range was as far as 20 feet, I doubt it would last very long, maybe a couple hours, max.
Remember, any radio transmitter has to compete with allot of other signals from dozens of sources, which means you need more power to get more range. The greater the range, the more power is needed. A satellite is Miles above us in Space!