Starting with the Series 6, the Apple Watch includes a built-in blood oxygen sensor (SpO2) that periodically measures the oxygen saturation of your blood throughout the day and night. While this can provide interesting wellness data and help track sleep patterns, the sensor shines a bright red LED light against your wrist to take its readings. If you find this light distracting at night, or if you simply do not care about tracking your blood oxygen and want to squeeze every last drop of battery life out of your device, you can completely disable the sensor.
How to Disable the Blood Oxygen Sensor
You can turn off the sensor either from your iPhone or directly on the watch itself. Using the iPhone is generally easier.
- Open the Watch app on your paired iPhone.
- Ensure you are on the My Watch tab located at the bottom left of the screen.
- Scroll down the list of settings and tap on Blood Oxygen.
- At the top of the menu, you will see a master toggle switch labelled Blood Oxygen Measurements.
- Tap this switch to move it to the Off position (the green background will turn to grey).
Alternative: Disable Only Background Tracking
If you still want the ability to take a manual blood oxygen reading by opening the app, but you want to stop the watch from glowing red randomly throughout the day and night, you can leave the master switch On, but scroll down and disable the two switches under “Allow Background Measurements” (In Sleep Focus and In Theater Mode). This ensures the sensor only activates when you explicitly ask it to.