Here is a nifty gadget that allows athletes to keep a close eye on fluid and electrolyte losses as they exercise. The Nix Hydration Biosensor comes with a pod that transmits data to smartphones and a patch that collects sweat. Nix works with iOS devices and Garmin sports watches. It is also compatible with Apple Watch.
The pod weighs less than 0.5 ounces. It lasts up to 36 hours on battery. The Nix app shows real-time hydration notifications and post-workout hydration summaries. As you starts moving your body, Nix measures sweat rate, electrolyte loss rate, and sweat composition.