If your Apple Watch went mysteriously quieter on the health front over the last year and a half, today offers a small — and slightly odd — measure of relief. On August 14, Apple pushed an update that restores Blood Oxygen tracking for certain Apple Watch models in the United States. But the feature you remember isn’t exactly the one that left: Apple redesigned how the watch measures and displays blood-oxygen data so it no longer runs afoul of an import ban tied to a long legal fight.

Here’s how the new setup works: the watch still collects sensor readings, but the math — the measurement and the calculation that turn raw light readings into a blood-oxygen percentage — now happens on the paired iPhone. That means you won’t get an on-wrist readout the way you used to; instead, your Blood Oxygen results show up inside the iPhone’s Health app under the Respiratory section. To get that back, affected users must update to iOS 18.6.1 on the iPhone and watchOS 11.6.1 on the watch.

The outward behavior looks the same — occasional background readings and the ability to record values — but the experience has moved off the wrist and onto the phone. It’s a subtle UX shift, but one with obvious legal engineering behind it.

The work-around applies to Apple Watch Series 9, Series 10, and Ultra 2 units that were sold in the U.S. after the International Trade Commission (ITC) import ban took effect on January 17, 2024. If your watch was sold before that date — or you bought it outside the U.S. — nothing changed for you; those units kept the original, on-wrist Blood Oxygen feature. Apple says you can tell whether your watch is one of the “covered” models because the serial number ends in LW/A.

This all traces back to Masimo, a medical-device company that makes pulse oximeters and filed multiple legal actions against Apple beginning in 2020. Masimo accused Apple of infringing patents tied to pulse-ox technology and also alleged trade-secret misappropriation. In 2023 the U.S. International Trade Commission concluded that certain Apple Watches infringed Masimo’s patents and issued an import ban that led Apple to remove or disable the Blood Oxygen feature on affected U.S. inventory. Apple appealed that decision and has been fighting the rulings in court; Masimo’s patents tied to the dispute are not set to expire until 2028.

The Apple workaround is essentially engineering around the ITC’s findings by changing where the “infringing” part of the process happens: transfer the calculation to the iPhone and you’re no longer shipping watches with the disputed behavior embedded. U.S. Customs has, apparently, accepted that redesign as compliant enough to allow imports of newly produced watches with the feature disabled on the wrist but present via the phone.

If you’re a person who liked glancing at an SpO₂ percentage on your wrist, the experience will feel like a step back. Quick checks made with a tap on the watch are replaced by a slightly slower, phone-dependent workflow. For day-to-day wellness tracking — sleep, background trends, respiratory monitoring — most users will still get usable data in the Health app. For clinicians or users who relied on instant on-wrist readings in the field, the change could be an annoyance. Reviews and early hands-on reports describe it as a “two-device” experience: the watch gathers, the phone translates.

Apple’s rollout is targeted and limited: only Series 9, Series 10 and Ultra 2 units sold after the ban are in scope, and the feature appears to be tethered to the phone by software updates. So if you own an older watch — Series 6 through Series 8, or any model bought outside the U.S. or before January 17, 2024 — you should see no change.

This episode is a tidy case study in how intellectual property law can reach into product UX. Apple has steadily expanded health capabilities on the Watch since it debuted SpO₂ measurements with the Series 6 in 2020; those features are now a core part of Apple’s health pitch. But when a court or regulator finds that a particular implementation infringes someone else’s patent, the response is not always a simple licensing deal — sometimes the practical answer is design around, which Apple has attempted here.

For Apple, the stakes are larger than a single metric. Health functionality has become a major product differentiator for wearables — and a data point in Apple’s push into healthcare services. For Masimo, the dispute is about protecting IP and market positioning for medical-grade sensors. Until the courts issue a final resolution or those patents lapse in 2028, expect more clever engineering workarounds and legal jousting rather than a clean, immediate reconciliation.

If you have a Series 9, Series 10 or Ultra 2 and you bought it in the U.S. after January 17, 2024 (look for a serial ending in LW/A), update both your iPhone and watch to iOS 18.6.1 and watchOS 11.6.1 to get the redesigned Blood Oxygen feature — but don’t expect the same on-wrist convenience you had before. For everyone else, nothing really changed. Behind the scenes, though, this small UX tweak tells a larger story about how tech firms juggle innovation, regulation, and intellectual property when the law pulls one of the strings.