Blood oxygen
August 14, 2025 at 8:34 PM by Dr. Drang
Nobody comes here for Apple news, so I assume you’ve already heard that Apple has started activating the blood oxygen sensor on all Apple Watches with the sensor. Until today, watches sold in the United States after January 2024 had their sensors deactivated because of the Masimo patent. As mentioned in the linked press release, new versions of watchOS (11.6.1) and iOS (18.6.1) will work together to let you take readings on your watch and then calculate and display the blood oxygen level on your phone. I have some thoughts.
First, I agree with Warner Crocker that this new US Customs ruling smells like the shit Tim Cook ate last week in the White House. Warner made the point less crudely.
Next, because I bought my Series 9 Watch in the fall of 2023, before the earlier Customs ruling went into effect, I’ve always had the blood oxygen sensor active. So I read this part of the press release very carefully:
There will be no impact [from the OS updates] to Apple Watch units previously purchased that include the original Blood Oxygen feature, nor to Apple Watch units purchased outside of the U.S.
That’s nice to hear, but I’m going to wait a bit before updating to see if the “no impact” promise matches reality. I feel bad that my trust in Apple software has fallen this far, but that’s how it is.
Finally, I’ve often wondered about the difference in Apple’s treatment of the blood oxygen and temperature sensors. By default, you don’t get an actual temperature reading; instead you get a variation from your “baseline” temperature. And Apple is careful to call it “Wrist Temperature” instead of just “Temperature,” presumably because it doesn’t want you comparing it with the value you’d get from an under-the-tongue thermometer or the thermometer used at your doctor’s office.
You can get the actual temperature readings from your watch by digging a little into the Health app. My temperature readings are generally a few degrees lower than my normal temperature measured by normal means.
By contrast, Apple will happily show you your blood oxygen reading:
I don’t believe this is any more trustworthy than the temperature. 95% is sort of a median value from my Health data, and it’s not unusual to see values as low as 90%. If the finger sensor in my doctor’s office ever showed readings like this, it would raise eyebrows. I don’t think I’ve ever seen my blood oxygen level less than 98% from those sensors.
Why is Apple more concerned about approximate temperatures than approximate blood oxygen levels? Beats me.