https://www.sciencedaily.com/releases/2021/04/210429112249.htm

The device is a thermoelectric generator (TEG) that uses temperature gradients to generate power. In this design, researchers use the difference between the warmer body temperature and the relatively cooler ambient environment to generate power.

"This is a field with great potential," says corresponding author Qian Zhang of Harbin Institute of Technology, Shenzhen. "TEGs can recover energy that's lost as waste heat and thus improve the rate of power utilization."