Apple restored blood oxygen measurements to affected Apple Watch owners in the United States on August 14, 2025, more than a year after the company disabled the feature on newly sold watches because of a patent dispute with medical technology company Masimo.
The return was not simply a switch back to the original system. Apple introduced a redesigned implementation in which the Apple Watch still collects sensor data, but the paired iPhone performs the blood oxygen analysis and displays the result in the Health app.
When Apple announced the change, it applied to U.S. users of the Apple Watch Series 9, Apple Watch Series 10, and Apple Watch Ultra 2 whose watches had been sold without working Blood Oxygen functionality.
How Apple's Redesigned Blood Oxygen Feature Works
At launch, affected users needed to update the paired iPhone to iOS 18.6.1 and the Apple Watch to watchOS 11.6.1. Apple said sensor data collected by the Blood Oxygen app would then be measured and calculated on the iPhone rather than entirely on the watch.
Results can be viewed on the iPhone by opening the Health app and going to Respiratory > Blood Oxygen. Apple subsequently incorporated the redesigned experience into its continuing software support, so owners should now use the latest compatible versions of iOS and watchOS rather than treating 18.6.1 and 11.6.1 as permanent requirements.
According to Apple's current support documentation, Apple Watch models purchased in the United States on or after January 18, 2024 with affected U.S. part numbers perform Blood Oxygen data analysis on the paired iPhone. Apple identifies current affected part numbers as ending in LW/A or LS/A.
Apple Watches that had already been purchased with the original Blood Oxygen feature were not changed by the 2025 redesign, and watches purchased outside the United States were not affected by the U.S. patent-related restriction.
Why Blood Oxygen Was Disabled in the First Place
The dispute traces back to a complaint filed by Masimo Corporation and Cercacor Laboratories with the U.S. International Trade Commission in June 2021. The companies alleged that Apple Watches using light-based blood oxygen technology infringed patents covering wearable physiological measurement systems.
The USITC opened an investigation in August 2021. After the investigation and subsequent review, the Commission issued a final determination in October 2023 finding a violation of Section 337 of the Tariff Act and imposed a limited exclusion order affecting infringing Apple Watches.
The resulting import restrictions created a complicated series of sales interruptions and court proceedings in late 2023 and early 2024. The affected Apple Watch Series 9 and Apple Watch Ultra 2 briefly disappeared from Apple's U.S. sales channels before a temporary court stay allowed sales to resume.
After that temporary relief ended, Apple took a different approach. Beginning January 18, 2024, it sold redesigned U.S. versions of the Series 9 and Ultra 2 with Blood Oxygen functionality disabled. That allowed Apple to continue selling the watches while its legal challenges continued. The later Apple Watch Series 10 also entered the U.S. market under the restriction.
What Changed in August 2025
Apple said the August 2025 restoration became possible because of a new ruling from U.S. Customs and Border Protection. The important technical difference was that blood oxygen data collected by the watch would be processed on the paired iPhone and viewed there, rather than producing the measurement through the same implementation that had been at the center of the earlier import dispute.
This distinction matters because Apple's physical watches still contained the optical hardware needed to collect relevant sensor data. The earlier U.S. restriction did not require Apple to build an entirely different watch without the sensors; instead, Apple had disabled access to the disputed functionality on affected units.
Moving part of the process to the iPhone therefore gave Apple a way to restore useful functionality without simply reactivating the original implementation.
The Legal Dispute Continued After the Feature Returned
The August 2025 software update did not end the Apple-Masimo dispute. Masimo challenged the Customs decision and continued arguing that Apple's redesign should remain subject to the exclusion order.
In March 2026, the U.S. Court of Appeals for the Federal Circuit affirmed the ITC's original findings concerning the earlier Apple Watch implementation. That ruling upheld the underlying infringement determination rather than declaring that Apple's original Blood Oxygen system had been cleared.
The redesigned system was considered separately. In April 2026, the ITC ended a modification and enforcement proceeding concerning Apple's newer redesign after declining to review the administrative law judge's determination. As a result, the redesigned Blood Oxygen implementation was not subjected to a new import ban in that proceeding.
That distinction explains an otherwise confusing outcome: Apple lost its appeal concerning the original implementation, while its later redesign was nevertheless permitted to continue.
Blood Oxygen Readings Are Not a Medical Diagnosis
The Blood Oxygen app uses optical sensors to estimate the percentage of oxygen carried by red blood cells. Apple says an on-demand measurement normally takes about 15 seconds, with the user keeping the wrist flat and still during the reading.
However, Apple explicitly states that Blood Oxygen measurements are intended for general fitness and wellness purposes rather than medical use. A smartwatch reading should therefore not be treated as a diagnosis or as a substitute for a medical-grade pulse oximeter, clinical evaluation, or professional medical advice.
Wearable readings can also be affected by factors such as movement, watch fit, skin perfusion, wrist position, and environmental conditions. An unexpectedly low or repeatedly abnormal reading can be useful information to investigate, but the number alone cannot determine its cause.
What the Return Means for Apple Watch Owners
For affected U.S. customers, the 2025 update restored a major health and wellness feature without requiring a replacement watch. The main compromise is that the redesigned U.S. implementation depends more heavily on the paired iPhone: the watch gathers the relevant sensor information, while analysis and result viewing take place in Apple's Health app on the phone.
The change also brought Apple's U.S. lineup closer to the functionality available on watches sold elsewhere, although the software architecture remains different for affected U.S. units.
Most importantly, the story did not end with the initial August 2025 announcement. Later court and ITC decisions preserved the original patent ruling while separately allowing Apple's redesigned approach to remain available, making the iPhone-processed Blood Oxygen system the practical resolution for affected U.S. Apple Watch owners.
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