Item — HN Reader

Apple was in a patent dispute over this feature with Massimo. Their workaround is to calculate blood oxygen on the iPhone, using the sensors from Apple Watch.

The Apple Watch hardware is otherwise the same. The back of the watch shines light of a specific wavelength into your skin and measures the reflected light. Heart rate sensing uses green (525 nm) and infrared (850–940 nm) light; blood oxygen sensing added a red light at 660 nm in 2020.

The iPhone will now calculate the ratio of absorbed red to infrared light, then apply calibration constants from experimental data to estimate blood oxygen saturation.

More detailed writeup on how the technology works is here: https://www.empirical.health/metrics/oxygen/

1 comments

Interesting that a small change like that is enough to not make it infringe the patent anymore. I guess you have to be really careful when writing patents to cover as much implementation variations as possible.

Masimo does not have an overarching patent on pulse oximetry, as the overarching technology is several decades old. There are many manufacturers of sensors being used in many applications with various implementations, many of which are not covered by Masimo's patents. Masimo could not write a patent to cover significantly more implementation variations because they would not be granted the patent in that case.

Masimo does have patents on specific implementations of pulse oximetry and sued Apple for implementing specific patented features. This made their legal case pretty solid, but it also made it possible for Apple to continue providing pulse oximetry as long as they avoided the specific IP owned by Masimo.