How wrist heat becomes a little electricity
The PowerWatch uses a thermoelectric generator: a material that produces a small voltage when its two sides are at different temperatures. One side sits against warm skin; the other is exposed to cooler air. That temperature gap nudges electrical charge through the material, turning some heat flowing away from the body into electricity.
This is the Seebeck effect, the same basic phenomenon used in other devices that convert a temperature difference into electrical power. The watch does not extract energy simply because its wearer is alive; it needs a usable difference between the skin and the surrounding environment.
Why the power supply has limits
The generator produces only a modest amount of electricity, so the watch must use energy sparingly. Its electronics and display need to be designed around that small, variable supply rather than the larger bursts of power available from a conventional rechargeable battery.
Harvesting also depends on conditions. If the watch is removed, the skin contact is lost. If the watch and surrounding air are close in temperature, the generator has less of a gradient to work with. In either case, less energy is available, and the device may rely on stored energy or reduce what it can do.
What “battery-free” really means
A thermoelectric watch can avoid routine charging by continually collecting energy while it is being worn, but that is not the same as an unlimited power source. Its operation depends on the heat flow around the watch, the efficiency of the generator, and how much electricity its features consume. The clever tradeoff is that a tiny stream of harvested energy can keep a carefully designed watch running—without making its power supply independent of the wearer or the environment.
