Sean Hodgins enjoys ring smithing, a hobby he adopted from his grandpa, and loves building small electronic gadgets. So he combined his passions to make a ring that turns body heat into light. Hodgins milled a two-finger band out of aluminum—an excellent thermal conductor—to cradle a 6-millimeter by 3-millimeter Peltier module and custom circuit board. The Peltier module converts heat flowing from the ring into a small voltage, and the circuit board amplifies the current. For now, cold weather best illuminates an LED on the ring, but Hodgins is designing a new circuit to make it blink brightly at any temperature.