Apple Watch blood oxygen measurement is not very accurate.
In addition to invasive testing in hospitals, most blood oxygen tests are still performed with pulse oximeters, which are based on the principle of emitting a specific wavelength of light through a red LED + infrared LED.
Then the device receives the reflected or projected light, and the finger-clip oximeter uses the projected type, while the smartwatch and smart bracelet wrist devices, taking into account the transmittance and the strap, naturally not good to use the projected type, so they all use the reflected type.
But there are still differences in the accuracy of the two, we take Apple's Apple Watch as an example, when we look at the parameters, we can see that Apple's heart rate monitoring function is over the U.S. FDA certification, but its oxygen saturation monitoring is not certified, and most of the smart wearable devices have not been certified by the FDA for this function.
This point can also be seen in the domestic devices, such as Huawei's Watch GT 3 Pro ECG ECG analysis through the national NMPA Class II medical device certification, but through the certification of the wrist oximeter is almost nothing, even if there is also unrelated to smart wearable devices. You can see the smart wearable device program, to reach the medical level of blood oxygen measurement is still difficult.