From Fitbit
• [Heart Rate Tracking] The heart of it all—heart rate powers important data like calorie burn, sleep stages, resting heart rate & more. • [Resting heart rate] An important indicator of your heart health & fitness. In general, active people have a lower RHR. • [On-wrist Bluetooth calls] Answer calls on your wrist, send callers to voicemail and adjust volume (when your phone is nearby).