Here’s a design that Dracula would love: a subcutaneously-implanted, wireless digital tattoo display whose fuel cell is powered by blood. An entrant into the same Greener Design Competition as the gravity clock, the concept uses Bluetooth to communicate with your portable gadgets???or even devices implanted elsewhere in your body.

Jim Mielke’s concept would be implanted beneath the skin on your arm. It then taps into your bloodstream, converting the oxygen and glucose into…