The quickest reliable check is to open the Blood Oxygen app on the Apple Watch Series 9, complete a roughly 15-second measurement, and look for the result on the paired iPhone at Health > Search > Respiratory > Blood Oxygen. Then verify the watch’s exact part number, region, software, and age eligibility. This is especially important for U.S. units ending in LW/A, because Apple introduced a redesigned iPhone-based experience for applicable watches in 2025.
Short answer
To find out whether an Apple Watch Series 9 has Blood Oxygen available, use two checks:
- Open the Blood Oxygen app on the watch and try a measurement.
- On the paired iPhone, open Health > Search > Respiratory > Blood Oxygen and look for the saved result.
Then verify the watch’s exact Apple part number in the iPhone’s Watch app. This matters especially for U.S. watches: models purchased in the United States on or after January 18, 2024 with a part number ending in LW/A use Apple’s redesigned iPhone-based Blood Oxygen experience. They should not automatically be described as having no Blood Oxygen feature; after the required software updates, the watch measures the data, the paired iPhone analyzes it, and the result appears in the iPhone Health app.
1. Try the Blood Oxygen app
On the Apple Watch Series 9:
- Open the Blood Oxygen app.
- Tap Start.
- Rest your arm on a table or otherwise keep your wrist still.
- Wait for the approximately 15-second measurement to finish.
If the measurement completes and a result is saved, the watch has an available Blood Oxygen user experience. Measurements are normally viewed in the Health app on the paired iPhone rather than as a permanent result displayed directly on the watch.
If you cannot find the app, search for Blood Oxygen on the Apple Watch. Apple says that, where the feature is available, the app can be searched for and reinstalled from the App Store on the watch. The app may also be unavailable because of the watch’s region, software, configuration, or the user’s age—not necessarily because the sensor is defective.
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2. Confirm the result in the iPhone Health app
On the iPhone paired with the watch, go to:
Health > Search > Respiratory > Blood Oxygen
Look for a recorded measurement. For applicable U.S. Series 9 watches using Apple’s redesigned experience, this iPhone Health location is particularly important: the watch collects the sensor data, the paired iPhone performs the analysis, and the result is displayed in Health.
Make sure the iPhone is the one paired with the watch and that both devices have Bluetooth enabled and are signed in and connected normally. A missing result after one failed measurement does not by itself prove that the feature is unavailable. Try again while sitting still, with the watch worn snugly and the arm supported.
3. Check the exact Series 9 model and part number
The product name alone is not enough. Two Apple Watch Series 9 units can have different Blood Oxygen behavior because of their purchase region, part-number configuration, software, or the availability rules in the country where the feature is being used.
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- Open the Watch app.
- Tap My Watch.
- Go to General > About.
- Confirm that Model Name says Apple Watch Series 9.
- Find Model Number. It initially appears as an Apple part number beginning with M.
- Tap the part number to reveal the five-digit A-model number.
Apple’s model-identification instructions are useful for confirming that the watch is genuinely a Series 9 rather than relying on the seller’s description, case appearance, or packaging.
What the LW/A suffix means
For Apple Watch models purchased in the United States on or after January 18, 2024, Apple specifically identifies part numbers ending in LW/A as using the redesigned iPhone-based Blood Oxygen experience.
The LW/A suffix identifies the U.S. configuration and how Blood Oxygen data is processed. It does not, by itself, prove that the watch lacks the underlying optical sensor. The practical test is to install the required updates, use the Blood Oxygen app, and check the iPhone Health app for the result.
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| What you find | What it means |
|---|---|
| Blood Oxygen app opens, measurement completes, and a result appears in Health | The feature is available in the current setup. |
| U.S. Series 9 part number ends in LW/A | It is the U.S. configuration associated with Apple’s redesigned iPhone-based experience. Update both devices and check results in iPhone Health. |
| The app is missing | Check regional availability, software, age eligibility, and whether the app was removed before assuming a hardware fault. |
| The watch is labeled Series 9 but the model details do not match | Verify the watch’s identity and part number before relying on the listing or seller’s claim. |
Important U.S. change: advice from before August 2025 may be outdated
Older articles often say that later U.S. Apple Watch Series 9 models do not have Blood Oxygen. That is now too broad.
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Apple said the update did not affect units that already included the original Blood Oxygen feature, and it did not affect units purchased outside the United States. Therefore, do not use the blanket rule “a U.S. Series 9 bought after January 18, 2024 has no Blood Oxygen.” A more accurate rule is:
- U.S. LW/A configuration: update the paired iPhone and watch, then use the redesigned iPhone-based experience and check Health.
- Older U.S. units with the original feature: their existing Blood Oxygen behavior remains unchanged.
- Units purchased outside the U.S.: Apple says the 2025 U.S. change does not affect them, but availability still depends on the country or region.
Because feature behavior can depend on software and regional rules, the app test and the Health result are more useful than a simplified date-based statement.
4. Update both devices
Install the latest compatible versions of iOS and watchOS available for the specific iPhone and Apple Watch. For the redesigned U.S. experience described by Apple in August 2025, the specifically identified versions are iOS 18.6.1 and watchOS 11.6.1.
After updating:
- Restart the iPhone and Apple Watch if the app or Health record still does not appear.
- Open the Blood Oxygen app again and complete a measurement while staying still.
- Return to Health > Search > Respiratory > Blood Oxygen.
Do not interpret an old pre-update explanation as proof that a current LW/A watch is permanently excluded. Apple’s redesigned U.S. experience changed the practical result for affected units.
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5. Check country and region availability
Blood Oxygen is not available in every country or region. A Series 9 may have compatible hardware but still not offer the app or readings where Apple has not enabled the feature.
Check Apple’s current watchOS Feature Availability page for the country or region relevant to the watch and account. The country where you happen to be traveling is not the only factor. The watch’s configuration, purchase region, software, and Apple’s feature availability rules all matter.
Traveling to another country should not be treated as a reliable way to add or remove the feature. Check the watch’s part number and Apple’s current regional availability information instead.
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6. Check the age limitation
Apple says the Blood Oxygen app is not available to people under 18. This can explain why an otherwise compatible Apple Watch does not provide the expected app or result.
Age eligibility is separate from the watch’s model number and sensor hardware. If the watch belongs to or is set up for someone under 18, the missing feature may be an eligibility limitation rather than a defect.
Troubleshooting: the feature is not showing
The Blood Oxygen app is missing
- Confirm the watch is actually an Apple Watch Series 9 in Watch > My Watch > General > About.
- Check the country or region against Apple’s current availability list.
- Update the iPhone and Apple Watch.
- Search the Apple Watch App Store for Blood Oxygen and reinstall it if Apple makes it available.
- Check whether the user is under 18.
- Verify the part-number suffix, especially if the watch was bought in the U.S. as a used or refurbished unit.
The measurement will not complete
- Keep the wrist still for the full measurement.
- Support the arm on a table.
- Wear the watch snugly, with the back of the watch in contact with the skin.
- Try again in a well-fitting position rather than immediately concluding that the feature is unavailable.
A measurement completes but nothing appears in Health
- Confirm that the correct iPhone is paired with the watch.
- Check Health > Search > Respiratory > Blood Oxygen, not only the watch display.
- For a U.S. LW/A model, confirm that the iPhone and watch have the software needed for Apple’s redesigned experience.
- Restart both devices and perform another measurement.
- Recheck regional availability and the watch’s part number before treating the problem as a hardware failure.
Buying a used or refurbished Series 9
If you are comparing an Apple Watch Series 9 listing, do not rely on a photograph of the watch, the product title, or a general statement that “Series 9 has Blood Oxygen.” Ask the seller for:
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- A screenshot of Watch > My Watch > General > About showing the Model Name and part number.
- The original purchase country or sales region.
- The approximate purchase date, particularly for a U.S. unit.
- Confirmation that the Blood Oxygen app opens and that a test result can be found in the paired iPhone’s Health app.
Listings may not disclose the relevant LW/A suffix or the watch’s purchase history. If Blood Oxygen is important to your decision, treat unit-level verification as essential and be cautious about returns or listings that cannot provide it. The 2025 U.S. software change also means that a seller’s older claim that an LW/A unit “does not have Blood Oxygen” may no longer describe the current experience.
What the reading does—and does not—mean
Apple describes Blood Oxygen measurements as intended for general fitness and wellness. They are not a medical diagnosis and should not be used for self-diagnosis, treatment decisions, or replacing a clinician’s assessment.
The Apple Watch is not a substitute for emergency care, a clinical pulse oximeter, or medical advice. If you have symptoms or a health concern, contact an appropriate medical professional rather than relying on a watch reading. A separate fingertip pulse oximeter may be considered for a different purpose, but it cannot activate Blood Oxygen on the Apple Watch and should not automatically be treated as an equivalent or a replacement for professional care.
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- Verify the model: confirm Model Name is Apple Watch Series 9.
- Check the region: confirm Blood Oxygen is available in the applicable country or region.
- Check the part number: tap the M-prefixed number in the Watch app to reveal the A-model number, and note whether the part number ends in LW/A.
- Update: install current compatible iOS and watchOS; for the 2025 U.S. redesign, Apple specified iOS 18.6.1 and watchOS 11.6.1.
- Test: open Blood Oxygen, tap Start, and remain still for about 15 seconds.
- Confirm: look under Health > Search > Respiratory > Blood Oxygen on the paired iPhone.
If the app is absent or no result is saved, check the region, age limitation, software, and part number before concluding that the watch lacks the sensor or that it is defective.
Sources: Apple Support, “How to use the Blood Oxygen app on Apple Watch”; Apple Support, “Measure blood oxygen levels with the Blood Oxygen app”; Apple Support, “Identify your Apple Watch”; Apple Newsroom, “An update on Blood Oxygen for Apple Watch in the U.S.” (August 14, 2025); and Apple’s watchOS Feature Availability information.
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How do I check whether my Apple Watch Series 9 has Blood Oxygen?
Open Blood Oxygen on the watch, tap Start, keep the wrist still for about 15 seconds, and then check the paired iPhone under Health > Search > Respiratory > Blood Oxygen. Also verify the model and part number in Watch > My Watch > General > About.
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What does LW/A mean on an Apple Watch Series 9?
A U.S. Apple Watch model purchased on or after January 18, 2024 with a part number ending in LW/A uses Apple’s redesigned iPhone-based Blood Oxygen experience. After the required updates, the watch measures the data and the paired iPhone analyzes and displays it in Health.
Does a later U.S. Apple Watch Series 9 definitely lack Blood Oxygen?
No. Apple’s August 2025 update means that the blanket claim is outdated. Applicable U.S. LW/A units use the redesigned experience after updating the paired iPhone and watch. Confirm the result in the iPhone Health app.
Why is Blood Oxygen missing from my Apple Watch Series 9?
The feature is not available in every country or region, and Apple says the Blood Oxygen app is unavailable to people under 18. Outdated software, a removed app, or an unsupported configuration can also explain the problem.
Is Apple Watch Blood Oxygen medically accurate or diagnostic?
No. Apple says Blood Oxygen is for general fitness and wellness, not medical diagnosis or treatment. It does not replace a clinician, clinical pulse oximeter, or emergency care.
The Bottom Line
The reliable answer comes from combining the hands-on test with the unit’s part number. Try Blood Oxygen, check Health > Search > Respiratory > Blood Oxygen, and verify the Watch app’s model information. For U.S. Series 9 watches with a part number ending in LW/A, update both devices and look for Apple’s redesigned iPhone-based result rather than assuming the feature is missing.
