Facial recognition, and something MS did with a camera that would recognize someone’s bone structure...distance between knee and heel, and elbow and wrist and gait and... combine those with autho’ed persons data for a location and why would you need to implant a chip?
DK
Passive RFID seems impractical for use in tracking. It’s range is too short. It could, at best, record when you pass through a doorway or pass close by a receiver.
You’d need to implant an active powered tag to actually track anyone from any distance, I’d think.