Jaybird ReignAdvanced Active Fitness Recovery Band - Black - L/XL Recovery is a weapon. Understanding your fatigue and recovery is the key to getting you to your max and crushing it. With Go-Zone you get a score each morning that tells you how ready your body is to be active, and how far you can confidently push yourself. Reign understands your bodys fatigue and recovery by measuring your Heart Rate Variability (HRV), as well as your Activity and Sleep patterns. Automatically recognizes and displays your day by activity and sport. A powerful motivator to see when and how you get more active over time. Automatically recognizes your sleep and knows how much you need tonight to be fully rested and at your best tomorrow. Lifetime Waterproof Warranty & 5 plus day battery.