The picture on the left shows Hitachi's infamous mu chip, once heralded as the world's smallest RFID tag. Back in 2003, it was touted as the perfect size for embedding into currency, slipping into bullets, and even tagging humans. The siren song of this dot-sized tracker even lured the Malaysian government into buying rights to it.
These are interesting but the range on them is probably very small unless you've got a huge antenna coil in your reader or a very powerful amplifier. That reduces the threat that they could be abused.
