hDrop Gen 2 is a reusable, wearable hydration sensor that analyzes sweat in real time to precisely determine how much fluid and how many electrolytes (sodium and potassium) are lost during exercise. Unlike disposable patches, which only provide data at the end of a session, hDrop tracks hydration metrics second-by-second while you train, thanks to a proprietary reusable electrode: just rinse it after use, no need for replacements. It is applied to the triceps, chest, or heart rate monitor strap with an adjustable strap (provided in two sizes, M and L). Independent validation tests report 92.5% accuracy on sweat loss and 87% accuracy on sodium loss.