Implanted lights as a means of communicating with an external device?
(edit: strange, the post didn't get posted. I'll rewrite it)
Has anyone implanted LEDs with any success - would it shine through the skin with enough strength to be picked up by a sensor? More usefully, would an infrared light be able to do the same? If either of these are true then we can fabricate a sensor that can be used to communicate I/O with, for instance, a smartphone.