A court ruled that Apple arranged meetings with Masimo to discuss its technology and then used those meetings to poach staff.  

After the meetings, Jobs’ Mob hired several Masimo staff, including the company's chief medical officer. 

Masimo CEO Joe Kiano later expressed concern that Apple may have been trying to steal the company's blood oxygen sensor technology. The company describes itself as "the inventors of modern pulse oximeters," and its tech is used in many hospitals.

In 2020, the company sued Apple for stealing trade secrets and infringing 10 Masimo patents. The lawsuit asked for an injunction on the sale of the Apple Watch.

Apple has consistently denied the claims and recently hit back with a counterclaim, alleging that Masimo's W1 Advanced Health Tracking Watch infringes multiple Apple patents.  So far that has not done very well, and a US court has already ruled against Apple on one of the patent claims.

What is worrying for Apple is that Masimo can now request a ban on the US import of Apple Watches. If granted, this would effectively end Apple Watch sales in the US, as the company would not be allowed to bring in the devices from China.