Masimo’s share price tumbled 5.2% overnight after Apple announced it would reinstate a blood oxygen measurement feature on select Apple Watch models, despite an ongoing patent dispute with the US health technology company.

The update comes as Masimo is still waiting to finalise the sale of its audio business to Samsung-owned Harman International.

Apple’s move follows a recent meeting between CEO Tim Cook and Donald Trump, whose administration had previously imposed bans on certain Apple Watch imports.

The feature—removed in late 2023 after Masimo won a US International Trade Commission (ITC) ruling that deemed it a violation of Masimo’s patents—will return via iOS 18.6.1 and watchOS 11.6.1 updates. Apple says US Customs has approved the change, which uses a workaround: blood oxygen data will now be processed on a paired iPhone instead of directly on the watch. Results will appear in the “Respiratory” section of the Health app.

Apple will re-enable the feature for Series 9, Series 10, and Ultra 2 models in the US, including devices that shipped without it. The update means users can initiate a reading from the watch, but the calculation and display will occur on the iPhone.

Masimo has long accused Apple of poaching staff and misappropriating its pulse oximetry technology. Under former CEO Joe Kiani—a close associate of Joe Biden—Masimo rejected settlement talks with Apple, instead pursuing litigation that led to last year’s import ban on certain Apple Watch models.

The ITC ruling forced Apple to temporarily remove the feature, but the company quickly secured a pause on the ban through the Federal Circuit. Masimo launched its own blood oxygen tracking device, the W1 watch, in 2022—two years after Apple first introduced the capability in its Series 6 watches.

This latest development arrives just weeks before Apple’s expected unveiling of new Apple Watch models and the iPhone 17. Restoring the blood oxygen feature will allow Apple to once again market it alongside other health tools, such as heart rate monitoring, in its push to dominate the wearables market.