Invention: Edible RFID:

RFID tags are tiny radio chips that resonate with a single echo when hit with a radio trigger. Kodak’s digestible tags are harmless and intentionally fragile. The tags would be covered with soft gelatin that takes a while to dissolve in the stomach. After swallowing a tag a patient need only sit next to a radio source and receiver.

And goddamn it I wrote that into a script last December!