On the tattoo, an ATiny85 microcontroller stores and receives data from temperature sensors via electro -conductive paint. There’s also room on there for an ambient light sensor that illuminates LEDs when it’s dark. And unlike a fitness tracker, you can mount it on places other than your wrist. The tech tattoos could be used to monitor a child’s vitals after a surgery, or provide a less public (or more, if you choose) display of fitness tracking.