According to a new study published in Nature Materials, flexible electronic sensors, worn like temporary tattoos on the skin, could be used to detect everything from blood flow to cognitive function.

The wearable sensors in the study were accurate to the same degree as the “gold standard” technology, a $250,000 infrared camera. But unlike the camera, the patch can do continuous monitoring without the need to maintain a line of sight.

Using just the temperature sensors, it’s able to see when a subject was working out math problems in one’s head, based on minute changes in metabolism. This functionality could potentially be used for lie detectors. It’s also able to track small physiological changes — a patch on a subject’s left hand could detect the subject rubbing one’s thumb and forefinger together on the right hand.

The electronics in the sensors could also convert them into actuators, generating one to two degrees of heat. Using a combination of actuators and temperature sensors, researchers could assess blood flow and skin conductivity, and extrapolate things like hydration.

Temperature sensors could be built into wearable devices along with other sensors. It adds into a pool of measurement modalities that could be really valuable.