By analyzing your sweat, you can learn more about your body, including fatigue and hydration level. The AbsolutSweat S1 is a smartphone connected sweat analyzer that gives you more insight into your health. It measures glucose, sodium, potassium, and other biomarkers and recommends how you can replenish electrolytes after a tough exercise session.
The S1 tracks your sweat rate and electrolytes in real-time and gives you recommendations prior, during, and after exercise. It also has a SDK for developers. You can find out more about this project on Indiegogo.