Radio transmitters to track merchandise are one thing, but are people ready for ID imbedded in their bodies? It is the technology that is everywhere and no place. It is invisibly inserted into the perky keyless remote that unlocks your car. It opens the garage door. It is wedged in the pass cards that let employees into office buildings. Subtle and controversial, the radio frequency identification device, or RFID, makes our lives more convenient in myriad small ways. But on a larger scale, critics warn that these dime-sized radio transmitters will one day become digital tattle-tales, a tool of what...