How can you power a wearable with just your fingertips?

Sweat-powered wearables are nothing new, but until now, you had to be active in order to generate enough sweat for them to be effective. That was something that a team of engineers at the University of California, San Diego set out to change with their latest sweat power-generating tech.

The result is a small Band-Aid-like device that can be stuck over the fingertip. Each of our fingertips contains more than a thousand sweat glands and can produce 100 to 1,000 times more sweat than most other parts of the body. You don’t usually notice because your fingertips vent really well, so most of the sweat evaporates right away. So if you could capture it before it does, that would be a pretty much effortless way to generate power.

In a test of their device, the team found that during 10 hours of sleep while wearing it, the subjects generated about 400 millijoules of energy, enough to power an electronic watch for 24 hours. “Compare this to a device that harvests energy as you exercise,” said Lu Yin, co-first author of the study. When you are running, you are investing hundreds of joules of energy only for the device to generate millijoules of energy. In that case, your energy return on investment is very low. But with this device, your return is very high. When you are sleeping, you are putting in no work.”