A new sticker-like patch could help people track their health and physical performance. The wearable sensor works by detecting chemicals in a person’s perspiration.

Four circles at the device’s center change color depending on the amount of certain chemicals in sweat. “The levels of these chemicals can indicate dehydration or oncoming muscle cramps,” says Ahyeon Koh, a biomedical engineer at the University of Illinois and one of the developers of the patch.

A smartphone app analyzes the color changes and relays the data to the wearer. “Professional athletes and even soldiers could use it to stay in peak condition,” says Koh. He and his colleagues hope the patch will be available to the public in the next year or so.