How do I check spO2 levels? And can these be monitored continuously?
Depends on the watch. Some do not have any PulsOx sensors, others do. But at those that have the PulseOx sensor, you can use the PulseOx widget for the measuring, and at most of them you can also set it up for continuous mode during night, or during all the day. The exact way, how to get to the widget, and to the settings depends on the model you own, and it it always well described in the user manual. Just note, that the PulseOx sensor is very power hungry, so it will drain your battery quickly, if permanently on.
