Apple Watch glows red from underneath, but no blood oxygen results.

Question

Level 1

11 points

Apple Watch glows red from underneath, but no blood oxygen results.

Hello,

So ever since I got my Apple watch series 11 I’ve sometimes notice that it glows red from underneath. I know this means that it’s measuring my blood oxygen levels but when I go and check results it doesn’t show. It just says for example: 15 hours ago, 12 hours ago etc.

When I notice that It’s measuring my blood oxygen levels I do not move the hand and wait for the red light to go out. If I go and measure it manually then it shows me the result.

Also, measurement is not affected while sleeping.

why does this happen? I just wanna know why my watch randomly glows red and does nothing after that.

I searched on google, asked ChatGPT but I couldn’t find the answer. Thats why I’m asking here.

(Both iPhone and Apple Watch are updated to latest software)

Thanks in advance!

Apple Watch Series 11, watchOS 26

Posted on Sep 10, 2026 6:00 PM

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Answer 1

ckuan

Level 10

122,338 points

Sep 10, 2026 6:15 PM in response to 4LukaLuka4

Measure your blood oxygen level

The Blood Oxygen app periodically measures your blood oxygen level throughout the day if background measurements are turned on, but you can also take an on-demand measurement at any time.

Go to the Blood Oxygen app on your Apple Watch.
Rest your arm on a table or in your lap, and make sure your wrist is flat, with the Apple Watch display facing up.
Tap Start, then hold your arm very still during the 15-second countdown.
At the end of the measurement, you receive the results. For models of Apple Watch purchased in the United States on or after January 18, 2024 with part numbers ending in LW/A, results cannot be viewed on Apple Watch, and are exclusively available in the Health app on iPhone. Tap Done.

Note: To get the best results, the back of your Apple Watch needs skin contact. Wearing your Apple Watch not too tight or too loose, with room for your skin to breathe, and flush with the top of your wrist, helps ensure successful Blood Oxygen measurements. For more information, see the Apple Support article How to use the Blood Oxygen app on Apple Watch.

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Answer 2

ckuan

Level 10

122,338 points

Sep 10, 2026 6:29 PM in response to 4LukaLuka4

The Blood Oxygen app periodically measures your blood oxygen level throughout the day if background measurements are turned on, but you can also take an on-demand measurement at any time.

If you want you can:

Turn off background measurements when the Sleep Focus or Theater Mode is active

Blood oxygen measurements use a bright red light that shines against your wrist, which may be more visible in dark places. You can turn off measurements if you find the light distracting.

Go to the Settings app on your Apple Watch.
Tap Blood Oxygen, then turn off In Sleep Focus and In Theater Mode.

If it on you can:

View your Blood Oxygen measurements history

Go to the Health app on your iPhone.
Tap (Lupe icon), tap Respiratory, then tap Blood Oxygen.

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Answer 3

BobHarris

Level 9

58,499 points

Sep 11, 2026 6:35 PM in response to 4LukaLuka4

There is a nice Apple Watch app, called "O2 Buddy" that can get your Blood Oxygen reading from your iPhone and display them on your Apple Watch. It is "Paid" app, but I've found it is useful, and paid for my copy.

https://apps.apple.com/us/app/o2-buddy-blood-oxygen-spo2/id6751239297

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Answer 4

MrHoffman

Level 10

163,273 points

Sep 10, 2026 6:30 PM in response to 4LukaLuka4

The infrared light is used for respiratory checks including sleep apnea, pulse rate, and oximetry monitoring.

Put differently, it apparently wasn’t monitoring SpO₂ right then.

And the monitoring involves the iPhone on recent Watch models.

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Answer 5

4LukaLuka4 Author

Level 1

11 points

Sep 10, 2026 6:22 PM in response to ckuan

This did not answer my question. I know that my Apple Watch measures SpO2 on the background. My question was why can’t I see the results after measuring is done.

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