As wearable Health Tech devices get smaller and smaller, how do you control them? Sure, they may send data wirelessly to an app running on a nearby smartphone, but there are circumstances where you might want to send a command or receive a notification from a device without having to reach for an external device.

Researchers at Saarland University in Germany and Google have developed a new approach to creating temporary electronic tattoos that can be use as inputs or outputs for digital devices. Using PEDOT:PSS, a conductive plastic, they are able to create thin film devices on temporary tattoo paper using simple screen-printing techniques. The result is thinner than a human hair, and is flexible enough to conform to the wrinkles in a typical human finger joint. This can be used for a variety of inputs. Bending your finger could signal a certain action. Touching a finger or hand in different places could produce different input signals. And by pairing the system with electroluminescent materials, the device can also light up to provide feedback to the user.

This technology could lead to nearly-invisible input mechanisms for wearable devices, helping smart systems “disappear” into our lives yet standing at the ready for us to issue intuitive and easy commands whenever we want.