Galaxy Note 4 will measure your oxygen saturation, significant health implications - iMedicalApps
So Samsung Health updated a few days ago and I seen this option to measure SpO2 while you sleep. I toggled it on and followed, the very few, instructions they gave for
Pulse Oximeter - Beat & Oxygen - Apps on Google Play
Note 4 - Oxygen Saturation Accuracy Test (holding my breathe) - YouTube
Measure Blood Oxygen Level and Heart Rate on Galaxy Watch | Samsung Developers