Apple’s latest iterations of the Apple Watch series come with a built-in pulse oximeter — a sensor that can measure blood oxygen saturation. Oxygen saturation indicates how much oxygen is reaching the organs in the body and provides insights into your overall fitness. This feature is beneficial to people with cardiovascular and respiratory problems like sleep apnea and even infections like pneumonia.

Since the Coronavirus pandemic, the Apple Watch has proved to be a must-have device for most people as it can detect oxygen-related problems, especially in those affected by COVID-19. Although Apple maintains that this feature is not for curative purposes, it can provide timely information that could help save lives. The average blood oxygen saturation is between 95 and 100%, and levels below 94% can be dangerous.

Standard oximeters can track blood oxygen levels when placed on a fingertip. But, the Apple Watch’s built-in oximeter measures oxygen levels at the wrist. When clipped to the fingertip, a standard pulse oximeter projects infrared light on one side of the fingertip. It then detects oxygen concentration on the other side of the fingertip.

The Apple Watch works similarly by measuring blood oxygen levels using infrared light. The blood oxygen sensor beams red, green, and infrared lights onto the wrist; the reflected light from four detector photodiodes is then used to perform calculations using advanced algorithms to determine the color of your blood.

The blood oxygen feature is available on Apple Watch Series 6 and Series 7, and the accompanying Blood Oxygen app is available for people 18 years and above.

Before using the Blood Oxygen app, you’ll need to ensure you have the latest versions of watchOS and iOS on your Apple Watch and iPhone.

To set up the Blood oxygen app, follow these steps:

  • Open the Health app on your iPhone.
  • Follow the steps on the screen, or tap on Browse> Respiratory> Blood Oxygen.
  • Tap Enable to complete setup.
  • On your Apple Watch, locate and open the Blood Oxygen app. If not available, you can download it from the App Store to your Apple Watch.

To measure your oxygen saturation, ensure the Apple Watch is facing up and fitting snugly on your wrist, not making contact with your wrist bone. Then, open the Blood Oxygen app and follow the instructions. Apple recommends keeping your arm on a table or lap as the watch takes the reading. The readings automatically sync to the Apple Health app on your iPhone.

The Apple watch can also take periodic measurements throughout the day, running in the background when you are idle, in bed, or on a couch. You can activate this setting in the Blood Oxygen app using these steps:

  • On your Apple Watch, go to Settings.
  • Select Blood Oxygen.
  • Turn on In Sleep Focus and In Theater Mode to activate.

If you wish to measure your blood oxygen levels only while asleep, you can turn on the Track Sleep With Apple Watch setting in the Health app.