The PowerWatch is a body heat-powered smartwatch that does very little
 

One of the biggest problems with smartwatches is avoiding a dead battery. Whether it's forgetting to plug them in in time, or having to fiddle with the unwieldy magnetic disk chargers, keeping a wearable juiced up is not as convenient as it should be...

https://www.engadget.com/2016/11/14/...atch-hands-on/