A new wearable device could one day transform your body into a human battery.

Researchers have invented a gadget that’s stretchy enough to wear like a ring, bracelet or other accessory that touches your skin. It works by tapping into a person’s natural heat, using thermoelectric generators to convert the body’s internal temperature into electricity. The device is part of a growing number of new battery technologies that could supercharge personal tech.

“Chips are getting more efficient, but you’re unlikely to get through the day without charging your phone,” said Andrew Fox, founder of electric scooter charging company Charge, in an email interview.

“It will be a while before our phones last two or three days, but there are promising signs.”