Continuous Heart Rate

Spot checks miss the pattern, while all day sampling shows resting trends.

Sleep Stage Tracking

Nights are the hours you cannot observe yourself, so the watch has to log them.

Blood Oxygen Readings

Overnight oxygen numbers add context that heart rate alone does not give.

Long Term Trend History

One day of data says little, so months of history in an app matter more.

Battery for Overnight Wear

A watch charging at bedtime records nothing, so multi day runtime helps.