ECG WITH CHEST STRAP: Daily measurement of ECG data, the chest strap comes with the watch that you can monitor the data on the wrist during the day and on the chest at night. Keep detecting your health all the time. BLOOD OXYGEN SATURATION (SpO2): Wear it on your wrist and instantly display your SpO2 on the watch. Measure AUTOMATICALLY, track oxygen saturation while sleeping overnight (midnight to 7 a.m.) and get SpO2 data all night long on our free app. Incredibly easy to use. HEART RATE VARIABILITY (HRV): Fitness Activity Tracker tracks your HRV overnight, making it a particularly useful tool for tracking your HRV. Good blood oxygenation is necessary to provide the energy your muscles need to function, which increases during sports activity. ALL-DAY ACTIVITY TRACKING: Track steps, distance, calories burned, active minutes and hourly activity. Support stopwatch, countdown on activity tracking during sport. CALL NOTIFICATION: Vibration alerts for call and text notifications, Facebook, Twitter, Gmail and other social network app notifications, motion reminders and alarms. WIDE COMPATIBILITY: Fitness Activity Tracker is compatible with smartphones Android 4.4 or later with Bluetooth 4.0 and running iOS 8.0 or later (iPhone 4 or later) not compatible with Windows Phone, all tablets, PC, computer laptop, iPad. Normal charge for about 1.5 hours. Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement.