The Amazfit GTS 2e smartwatch features a more sophisticated circuit design, a thinner body and a high-capacity battery that stays active for up to 24 days of typical use. The BioTracker 2 optical sensor developed by Huami enables 24-hour heart rate monitoring. It covers heart rate zones and alerts you if your resting heart rate is abnormally elevated. The GTS 2e sports watch provides in-depth sleep monitoring that distinguishes between the light depth and REM sleep periods. It monitors sleep breathing status, provides quality analyses and suggestions for improvement based on a night's sleep and detects daytime naps over 20 minutes. Note: Sleep of less than 20 minutes is not recorded.