A stretchable stopwatch lights up human skin

Imagine a runner who doesn't need to carry a stopwatch or cell phone to check her time: She could just gaze at the glowing stopwatch display on the back of her hand. Such human-machine interfaces are no longer science fiction, but they still have a way to go before becoming mainstream. Now, researchers have developed a stretchable light-emitting device that operates at low voltages and is safe for human skin.