Ever use the expression “sweating buckets” after a tough workout? It doesn’t have much literal meaning, but if you ever looked for a way to quantify your perspiration, this new tech might interest you. Researchers have created a soft adhesive patch that can measure the composition of your sweat, they report today in Science Translational Medicine. You can scan the patch with your smartphone and an app will give you information about your electrolyte balance, dehydration levels, and total water loss. It works like this: As your pores release sweat, a ring-shaped channel fills up and diverts into four different sensors that absorb the moisture. Each sensor has a corresponding color—blue, yellow, orange, or red—and each one measures something different: chloride, glucose, pH, or lactate. The color becomes more vibrant based on the concentration of what it monitors. Measuring electrolyte loss can combat fatigue, and tracking chloride ions can indicate susceptibility for diseases like cystic fibrosis. With a little tweaking, the patch could even be used to test for doping at athletic events, the authors say.