Many wearable biosensors, data transmitters and similar tech advances for personalized health monitoring have now been “creatively miniaturized,” says materials chemist Trisha Andrew at the University of Massachusetts Amherst, but they require a lot of energy, and power sources can be bulky and heavy. Now she and her Ph.D. student Linden Allison report that they have developed a fabric that can harvest body heat to power small wearable microelectronics such as activity trackers.