I didn’t think it was possible but MIT researchers have actually done it. Its based on a concept that NASA originally used where their space probes harvested heat from radioactive plutonium. Semiconductors can produce a similar effect between its hotter and colder sides and Enocean have a patented bit of kit that does just that. These self powered sensors are the start of devices that don’t need batteries!
es! This MIT news article explains this in greater detail.
In this video North Carolina State explains how they are creating Self-Powered and Wearable Health Monitors