For example, could the technology track every person riding a bus if everyone inside that bus wore a passive UHF RFID badge tag?
You might be able to read a few of the tags, but you would almost certainly not be able to interrogate them all. In general, it is difficult to read passive ultrahigh-frequency (UHF) RFID tags in badges, because the human body is mostly composed of water, which absorbs RF energy and would prevent that energy from reaching the tag. Battery-assisted passive UHF tags would work better for this application. The second issue is that a bus is made of metal, and energy would bounce off the side of the bus and be reflected away from any tags inside of it. It would make more sense to try to read the badge tags as riders entered the vehicle.
—Mark Roberti, Founder and Editor, RFID Journal
Where Can I Learn About RFID-Chipped ID Plates? »