Fitbit Alta HR Fitness Tracker with Heart Rate, 7 Day Battery Life, Compatible with Smartphones, Tablets, Computers Only worn for month Still works and charges Small Get the power of continuous heart rate in Fitbit's slimmest design yet-all day, during workouts and beyond With heart rate, you can better measure calorie burn, and use zones (fat burn, cardio, and peak) to find the right workout intensity for your goals See how working out more can improve your health by comparing your resting heart rate trends to your activity With sleep stages powered by purpose heart rate, automatically track your time spent in light, deep and REM sleep and take steps toward a better night's rest Automatically track your steps, distance, calories burned and active minutes with up to 7 days of battery life