iOS 18.6.1 alone does not enable Blood Oxygen. The redesigned U.S. feature requires an eligible Apple Watch Series 9, Series 10, or Apple Watch Ultra 2 that previously lacked Blood Oxygen, iOS 18.6.1 on the paired iPhone, and watchOS 11.6.1 on the watch. Once updated, install or open Blood Oxygen on the watch; the iPhone calculates the reading and shows it in the Health app.
Blood Oxygen was not enabled by iOS 18.6.1 alone. For the redesigned U.S. experience announced by Apple on August 14, 2025, you need an eligible U.S. Apple Watch Series 9, Series 10, or Apple Watch Ultra 2, plus iOS 18.6.1 on the paired iPhone and watchOS 11.6.1 on the watch. After updating, the watch collects the sensor data, while the paired iPhone calculates the result and stores it in the Health app.
This rollout was specific to certain U.S. watches that previously did not have Blood Oxygen. It did not add the feature to watches purchased outside the United States, and it did not change Apple Watch units that already had the original Blood Oxygen feature.
Before you start: check whether your watch qualifies
For the specific iOS 18.6.1 activation path, Apple named these U.S. models:
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- Apple Watch Series 9
- Apple Watch Series 10
- Apple Watch Ultra 2
The watch must be a U.S. unit that previously lacked Blood Oxygen. A Series 9, Series 10, or Ultra 2 purchased in another country is not made eligible merely by changing the iPhone’s region or installing the update.
Apple’s broader support information describes the Blood Oxygen app as supported on Apple Watch Series 6 or later and all Apple Watch Ultra models, while excluding Apple Watch SE and Apple Watch For Your Kids. That broader compatibility statement should not be confused with the special U.S. iOS 18.6.1 rollout: model, country or region, purchase history, and software version all matter.
The Blood Oxygen app is also unavailable in some countries and regions, and Apple says it is not available for people under 18. If the feature is unavailable in your region or for your account, updating will not activate it.
What you need to install
- An eligible, paired Apple Watch.
- An iPhone XS or later for iOS 18.6.1.
- iOS 18.6.1 on the iPhone.
- watchOS 11.6.1 on the Apple Watch.
- Enough battery and time for both updates to finish.
Apple released iOS 18.6.1 and watchOS 11.6.1 on August 14, 2025. Because later software may now be offered, your iPhone or Watch app may direct you to a newer compatible release instead. If you are following the original version-specific procedure, the required pair is iOS 18.6.1 and watchOS 11.6.1; for current troubleshooting, Apple’s general guidance is to use the latest compatible iOS and watchOS versions.
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How to enable Blood Oxygen with iOS 18.6.1
- Update the paired iPhone. Open Settings > General > Software Update, then install iOS 18.6.1 if it is available. Keep the iPhone connected to power if the update requires it.
- Update the Apple Watch. On the iPhone, open the Watch app and go to My Watch > General > Software Update. Install watchOS 11.6.1, or the latest compatible watchOS version offered for the watch. The watch normally needs to be on its charger, within range of the iPhone, and sufficiently charged.
- Look for Blood Oxygen on the watch. Open the app grid or list of apps on the Apple Watch and search for Blood Oxygen. If it is missing, open the App Store on the watch, search for Blood Oxygen, and download it. If the app was deleted, it can be installed again from the watch App Store.
- Open Blood Oxygen and follow the prompts. The app will guide you through its setup. On the affected U.S. models, the watch gathers the sensor information but the paired iPhone performs the analysis and displays the result in Health.
- Take a reading. Wear the watch correctly, open Blood Oxygen, tap Start, and hold your arm still for the 15-second countdown.
If you need an eligible replacement rather than an activation, Apple explicitly included the Apple Watch Series 9, Apple Watch Series 10, and Apple Watch Ultra 2 in the U.S. rollout. Confirm the exact model’s country and feature availability before buying: purchasing one of these watch families does not guarantee Blood Oxygen availability in every market, and the feature is intended for wellness rather than diagnosis.
How to take an accurate on-demand reading
For the 15-second measurement:
- Wear the watch snugly but comfortably, with its back touching your skin.
- Move it one to two inches above the wrist bone if the bone prevents the sensor from sitting flush.
- Open the Blood Oxygen app and tap Start.
- Rest your arm on a table or in your lap.
- Keep the palm facing down and the wrist flat, with the watch face pointing upward.
- Remain completely still until the countdown ends.
A practical preparation accessory can help only with the update or fit—not with enabling the feature. For example, an Apple Watch magnetic charging cable can keep the watch powered during installation, but no charger unlocks Blood Oxygen. Likewise, a snug Apple Watch band may help maintain skin contact, but Apple does not establish that any particular third-party band improves measurement accuracy.
Where to see Blood Oxygen results
On the paired iPhone, open:
Health > Search > Respiratory > Blood Oxygen
Apple says both on-demand and background measurements are saved there. You can view day, week, month, and six-month trends, and filter readings taken during sleep or at high elevation.
For the affected U.S. watches purchased on or after January 18, 2024 with part numbers ending in LW/A, Blood Oxygen analysis occurs on the iPhone and the results are viewed in Health. This is why the feature may not behave like a fully self-contained watch app: the watch is collecting the data, but the paired phone is doing the calculation.
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How background readings work
Background readings may be taken when you are not moving. Sleep measurements occur only when Track Sleep with Apple Watch is enabled.
On the watch, open Settings > Blood Oxygen to review controls for background recordings during Sleep Focus and Theater Mode. If you want overnight data, check that sleep tracking is enabled and that the watch is worn during sleep.
What to do when Blood Oxygen will not read
A failed or inconclusive measurement does not necessarily mean the sensor or watch is defective. Apple identifies several causes of unreliable readings, including cold conditions, inadequate skin perfusion, tattoos, movement, certain arm or finger positions, a loose fit, and a resting heart rate above 150 beats per minute.
Try this sequence:
- Warm your wrist. Cold skin can reduce the quality of the reading.
- Improve contact. Tighten the band enough for steady skin contact, but not so much that it is uncomfortable.
- Move the watch above the wrist bone. Position it one to two inches above the bone if the sensor is not sitting flush.
- Settle your arm. Rest it flat on a table or in your lap, with your palm down.
- Stop moving. Keep still for the entire 15-second measurement.
- Try again at rest. A high resting heart rate can interfere with a reliable result.
If the Blood Oxygen app is missing
- Check whether Blood Oxygen is available in your country or region.
- Search for Blood Oxygen in the App Store on the Apple Watch.
- Reinstall it from the watch App Store if it was deleted.
- Confirm that both the iPhone and Apple Watch are updated.
- Confirm that the watch is paired with the iPhone you updated.
- Recheck the model and U.S. eligibility requirements.
Apple’s documentation does not promise that every eligible watch will display the feature immediately after updating. If the app remains absent after checking the region, model, pairing, and software, do not assume that repeatedly reinstalling it will override an eligibility restriction.
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Important limitations: Blood Oxygen is not a diagnosis
Apple says Blood Oxygen measurements are intended for general fitness and wellness, not medical use. They are not intended for self-diagnosis or for deciding whether to consult a doctor.
Apple notes that many people have readings between 95% and 100%, but some healthy people normally measure below 95%, and readings can be lower during sleep. A single Apple Watch result should not be treated as a diagnosis or as a replacement for a medical pulse oximeter or professional medical advice. If you feel unwell or are concerned about your breathing or oxygen level, contact a healthcare professional rather than relying on the watch alone.
Quick eligibility checklist
- Is the watch a U.S. Apple Watch Series 9, Series 10, or Ultra 2 that previously lacked Blood Oxygen?
- Is Blood Oxygen available in your country or region?
- Is the user 18 or older?
- Is the paired iPhone an iPhone XS or later?
- Is the iPhone running iOS 18.6.1 or a later compatible version?
- Is the watch running watchOS 11.6.1 or a later compatible version?
- Have you searched the watch App Store if the app is not visible?
- Are the watch fit, skin contact, wrist temperature, and stillness suitable for a reading?
Frequently Asked Questions
Can iOS 18.6.1 add Blood Oxygen to any Apple Watch?
No. The iOS 18.6.1 rollout was for certain U.S. Apple Watch Series 9, Series 10, and Apple Watch Ultra 2 units that previously lacked Blood Oxygen. The watch and iPhone both need the appropriate software updates.
Where do I view Apple Watch Blood Oxygen results?
On the iPhone, open the Health app and go to Search > Respiratory > Blood Oxygen. On affected U.S. watches, the watch collects the data but the paired iPhone calculates the result.
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Why does my Apple Watch Blood Oxygen reading fail?
A cold wrist, loose fit, movement, tattoos, poor skin perfusion, an obstructed sensor position, or a resting heart rate above 150 beats per minute can interfere with a reading. Warm the wrist, move the watch above the wrist bone, rest your arm flat, and stay still for 15 seconds.
Is Apple Watch Blood Oxygen medically accurate?
No. Apple describes Blood Oxygen as a general fitness and wellness feature. It is not intended for medical use, self-diagnosis, or replacing a medical pulse oximeter or clinician’s advice.
The Bottom Line
To use the iOS 18.6.1 Blood Oxygen rollout, you need an eligible U.S. Apple Watch Series 9, Series 10, or Ultra 2, iOS 18.6.1 on the paired iPhone, and watchOS 11.6.1 on the watch. Install or reinstall Blood Oxygen from the watch App Store, then take readings in a snug, stable position and view the results in Health > Search > Respiratory > Blood Oxygen. The feature is regional, age-limited, and intended only for wellness—not medical diagnosis.
