I think the “30 second finger ECG sampling” is unique to the Apple Watch. Most modern continuous trackers use optical heart rate (PPG) alone. Garmin includes a

I think the “30 second finger ECG sampling” is unique to the Apple Watch. Most modern continuous trackers use optical heart rate (PPG) alone. Garmin includes a red light PPG that is used as a Pulse Oximeter during sleep to measure SpO2 and they also continuously monitor Heart Rate Variability (HRV) that they report as stress. Garmin also uses machine learning models to predict sleep stages with PPG data without an EEG. All of these consumer grade sensors are poor compared to the medical PPG, ECG, and EEG equivalents but they have the advantage of being ubiquitous and continuous. They offer the ability to collect a baseline for our health data that is supplemented with short samples during exceptional events.