Jaybird Reign Fitness Tracker (Black, L/XL)

Gain insight into your body's energy levels with the black Jaybird Reign Fitness Tracker in large/extra large. This smart wristband measures your activity and heart throughout the day and then gives you a score the next morning that tells you how ready you are for physical activity that day. This is accomplished by measuring the variability in time between each of your heartbeats with the built-in heart rate monitor and detecting patterns of fatigue or recovery.