That’s the idea behind a demonstration by John Rogers, a stretchable electronics pioneer at the University of Illinois at Urbana-Champaign, whose lab created a stretchy skin patch that uses light pulses to monitor heart rate or sun exposure.

Instead, it’s powered by a cell phone or tablet that’s equipped with a near-field communications chip, the kind that’s used in apps like Apple Pay or for sharing photos between phones.

That is, radio signals from a phone actually power the device and let it transmit information.

Rogers is a specialist inEpidermal electronics,” and he’s come up with variety of devices that integrate LEDs, tiny bits of electronics, and sensors onto stretchy materials where they’re wired up with spring-like metal wires.

A drawback of this system is that to power the device, the wearer must be within a few centimeters of a cell phone or tablet-or within a meter of a long-range NFC reader.

Most of us are never much farther from our devices anyway.

The need for a battery adds a millimeter or two of thickness to one of MC10’s other products, the BioStampRC, a device sold to researchers who want to monitor people’s health signs and biomechanics while they are on the go.