Sweat could fuel the future of wearable devices, said Timothy Revell at New Scientist​. Re­search­ers have figured out how to power a simple radio for up to two days with a skin patch that harvests energy from human sweat. The flexible patch, which is less than an inch across, "contains enzymes that replace the precious metals normally used in batteries" and feed off the lactic acid found in sweat.

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But "sweat radio isn't the end goal." Researchers hope to use the technology to build wearable sensors that monitor health conditions, using the sweat to generate enough power for a Bluetooth connection so that the results can be sent to a smartphone. "We're now getting really impressive power levels," says Joseph Wang at the University of California, San Diego. "If you were out for a run, you would be able to power a mobile device."