Researchers from the University of Illinois at Urbana-Champaign have discovered the next must-have item for physical fitness: a flexible stick-on patch that could monitor exactly when you need to rehydrate.

As reported in Popular Science, this new sweat monitor can be attached to the forearm or lower back to effectively measure electrolyte and glucose levels as well as the sweating rate of the body. Each stick-on circle has enzymes that react to your sweat's glucose, lactate, chloride, and pH levels, all of which could give a warning when the body is being overexerted. The stick-on patch works by absorbing sweat and channeling it through tiny capillaries to four circles at the center of the device. With all the data it processes, the patch is practically a laboratory attached to the body.

"We don't, right now, have an app with a user-friendly front-end interface," said John Rogers, the senior author of a new study on this new technology and a materials scientist at Urbana-Champaign. Rogers and his team are still developing an interface that would help users interpret the color data.

To test if the patches could perform in real-life exercise situations, the researchers gathered data from on a group of indoor bicyclists as well as 12 volunteers riding outdoors in the El Tour de Tucson in Arizona. The sweat monitors remained attached to the bicyclists, proving that they were effective in both conditions.

Developed to be inexpensive and disposable, each circle could monitor sweat for up to 6 hours with each use. This also depends on how much sweat is absorbed by the stick-on patch.

Rogers also hinted at other possible benefits of wearing the patch. "The devices could be used in athletic and military training to gain insight into critical electrolyte loss, thereby guiding earlier supplementation before symptomatic cramping and 'hitting the wall' points in time at which appropriate preventative treatment is no longer effective."

Though it may take a few years before the sweat monitors could be available to the public, it would certainly be a gadget to watch out for especially for people who lead an active lifestyle.