Researchers at the University of Illinois at Urbana-Champaign have developed a flexible patch that monitors if you need to rehydrate.

The new device is placed on your forearm or lower back. It absorbs sweat and tests for glucose, lactate, chloride and pH levels to determine if you are overworking your body. Circles in the patch will change colors as they test your sweat. A smartphone app analyzes the color of the circles and determines the contents of your sweat.

The patches are designed for a single use and can monitor sweat for up to six hours.

Although the design is still a few years away from completion, it could be used to warn athletes or military personnel when they are nearing overexertion before it’s too late.