There are many ways self-powered devices can work. One is piezoelectric energy, which is generated when you apply pressure to certain materials. Another method, more common in the public imagination, is harvesting movement. But while movement seems obvious, it’s not practical to have a device that only works when you’re in motion. So, for many researchers, the best source of energy is body heat, or thermoelectric generation.
Thermoelectric generation works because our bodies are almost always a different temperature from the air outside. Thermoelectric generators pick up on the temperature difference and then use that to create energy, says Daryoosh Vashaee, an electrical engineer at North Carolina State University. Last year, his team built a tiny device that did just that. It’s a metallic tab that can be embedded in a shirt or worn on an armband.