Scientists have come up with a device that harvests sweat from your fingertip to generate power. The flexible, thin strip wraps around the tip of a finger like a Band-Aid and converts chemicals found in human sweat into small amounts of electrical energy. Fingers constantly produce sweat, so the device can work without the wearer moving a muscle.

"By using the sweat on the fingertip -- which flows out naturally regardless of where you are or what you're doing -- this technology provides a net gain in energy with no effort from the user," said Joseph Wang, a professor of nanoengineering at UC San Diego and co-author of a paper describing the product, published Tuesday in the journal Joule.

It's common for self-powered wearable systems that rely on bioenergy harvesters to require excessive inputs of energy. But because this device doesn't require any physical input from the wearer to work, it's "a step forward to making wearables more practical, convenient and accessible for the everyday person," study co-author Lu Yin, a nanoengineering Ph.D. student at UC San Diego, said in a statement. UC San Diego researchers previously worked on temporary tattoos that turn sweat to power. 

While the new product can produce power, it's not time to kick your tangly cords and finicky electrical outlets to the curb just yet. The device can potentially power lower-power electronics that operate in the milliwatt range, such as a wristwatch, but it's not yet suitable for continuously powering high-performance electronics such as smartphones, the researchers say. 

"Our goal is to make this a practical device," Yin said. "We want to show that this is not just another cool thing that can generate a small amount of energy and then that's it. We can actually use the energy to power useful electronics such as sensors and displays."

Fingertips, each packed with more than a thousand sweat glands, can produce between 100 to 1,000 times more sweat than most other body parts. It might be hard to notice how sweaty they are, though, since the sweat typically evaporates from fingertips as soon as it comes out. This new device collects it before it can. 

The device was built to be highly absorbent. First, sweat is absorbed and converted into energy by a padding of carbon foam electrodes. The electrodes have enzymes that trigger chemical reactions between lactate and oxygen molecules in sweat, generating electricity. There's also a chip underneath the electrodes made of piezoelectric material that generates more energy when pressed.

Electrical energy is stored in a small capacitor as a wearer sweats or presses on it. It can then be discharged to fuel low-powered devices.  

As a subject slept for 10 hours with the device on a fingertip, the wearable collected 400 millijoules of energy, which is enough to provide 24 hours worth of power to an electronic wristwatch (but not a smartwatch). The researchers note that strapping devices to additional fingertips would generate even more energy. But I'm still processing the news about how many sweat glands are on ONE of my fingers, much less 10.