i have noticed on several occasions that my Apple Watch Series 9 goes red on the underside.
i have not noticed it during daytime but it has happened in the night around 2am and this morning around 8am.
What does this mean?
Apple Watch Series 9
This is the Blood Oxygen Sensor, which uses red light to measure the oxygen level in your blood.
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copied from: How to use the Blood Oxygen app on Apple Watch - Apple Support
This is the Blood Oxygen Sensor, which uses red light to measure the oxygen level in your blood.
...
...
copied from: How to use the Blood Oxygen app on Apple Watch - Apple Support
Apple Watch series 9 - why does it go red?
