Watch Pulse oximeter

It still works on my Apple Watch Ultra 2, which I did not buy in the US. And only models sold after January 18th in the USA are affected.

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• The ability to measure blood oxygen is no longer available on Apple Watch units sold by Apple in the United States beginning January 18, 2024. These are indicated with part numbers ending in LW/A. Learn how to identify your Apple Watch.

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copied from: Watch - Apple

There have been reports from U.S. Series 9 users that got their Apple Watch in November 2023 the the O2 sensor STILL WORKS after applying the 10.3 update. As well as Series 8 and 7 reports that it still works.

And reports that a Series 9, purchase AFTER January 19, 2024, where the O2 sensor was disabled.

So ONLY U.S. Series 9 and Ultra II Apple Watches, purchased after 19-Jan-2024 have the O2 sensor disabled.