Our bodies ooze energy in the form of heat. Infineon Technologies, a microelectronics company in Munich, Germany, has developed a dime-sized chip that converts this heat into enough electricity to power a small electronic gadget, which would otherwise rely on tiny and expensive batteries. One side of the “thermogenerator” faces the body, and the other faces the air; the temperature difference between the two sides produces a current. Unlike other heat-to-electricity devices, which are made out of expensive and toxic metals, Infineon’s chips are silicon-a cheaper and more benign material.Given a typical temperature difference at the wrist of 5 C, prototype devices can generate enough power for a wristwatch-around one microwatt per square centimeter-says Werner Weber, head of Infineon’s Laboratory for Emerging Technologies. Infineon is working with a watchmaker to incorporate the thermogenerator into the firm’s products. The chips, says Weber, could find their way onto the market in two years in watches or wearable medical devices; a thermogenerator embedded in a jogging suit, for instance, could power a heart sensor.