Nicole Wetsman for The Verge, ‘Apple Watch’s blood oxygen monitor is for ‘wellness,’ not medicine‘:
Most oxygen sensors, including Apple’s, measure the amount of oxygen in your blood using light. These devices are called pulse oximeters, and they typically clip on to your fingertip. A standard version sends both red and infrared light through the finger, where there’s lots of blood close to the surface. A protein in the blood absorbs more infrared light when it has oxygen and more red light when it’s doesn’t. A sensor on the other side of the finger calculates how much of each type of light travels through, providing an oxygen reading.
Apple Watch measures light reflections, which can be less accurate with lower levels of blood oxygen. So Watch users should treat the readings as more of a curiosity than a medical diagnosis?
I really thought, when they were playing that intro video about the woman with diabetes, that Apple was announcing diabetes monitoring. For a lot of these specialized health issues, that Apple should offer more specialized devices that sync with the Watch or iPhone, like an insulin pump or a blood pressure cuff. Sure, it’s not for everyone, but neither is the HomePod, if we’re being honest.