How Does The Apple Watch Measure Blood Oxygen 2022

How Does The Apple Watch Measure Blood Oxygen

Since the launch of the Apple Watch Series 6, users have been able to measure their blood oxygen levels directly from their Watch. The blood oxygen sensor which was added to the Series 6 comes paired with an app that you can download onto your watch and track your oxygen saturation levels in real-time.

Using this feature, you’re able to determine whether you have any underlying sickness and if your body is receiving the correct levels of oxygen. While all that sounds good, the main question still remains, how does the Apple Watch measure blood oxygen levels?

Well, i’m going to take you through everything you need to know about measuring blood oxygen levels using the Watch Series 6, how it works and even a couple of tips so you are able to receive accurate results.

Let’s begin!

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How Does The Apple Watch Measure Blood Oxygen

Before we get into the actual mechanism behind how the Apple Watch Series 6 measures your blood oxygen level, it’s important to first understand what blood oxygen means and why we’re keeping a record of its readings with the Apple Watch.

What is Blood Oxygen?

Blood Oxygen is a medical term given to the percentage of oxygen that’s present in your red blood cells as they travel from your lungs to various parts of your body. Healthy individuals would record an average blood oxygen level of 95% - 100, whereas others with health conditions may have a slightly lower reading.

It’s important to understand what the readings represent so you will be able to determine whether someone requires immediate medical attention or not.

Here’s how the Apple Watch Series 6 measures your blood oxygen levels.

How the Blood Oxygen Sensor Works on the Watch Series 6

With the Apple Watch Series 6, the optical heart sensor has been tweaked a bit to include blood oxygen measurement capabilities. Here, the red and green LED's fire an infrared light into your wrist where with the help of Photo-diodes, the Watch is able to measure the amount of light that’s reflected.

How Does The Apple Watch Measure Blood Oxygen

The Series 6 along with the blood oxygen app then uses advanced algorithms to determine the color of your blood. It’s this difference in color that indicates whether your blood oxygen levels are normal or if they are low.

Normally, light or bright red blood means there’s more oxygen present whereas, the darker the color of your blood would mean that there’s less oxygen present. 

Also Read: Apple Watch Series 6 hidden features

Prerequisites Before Setting up the Blood Oxygen App

In order for your Apple Watch 6 to measure and record your blood oxygen levels, there are a  couple of things to keep in mind. 

  • The first thing you need to do is to figure out whether the app is available in your country or region. Since it’s not available worldwide just yet, while setting up the Apple Watch and the Health app, you’d be able to see whether your country or region has blood oxygen capabilities as yet.
  • You will need to update your iPhone to the latest version of iOS. Also, in order for this to work, you would have to own any iPhone post the iPhone 6s and not earlier models as this feature is not available to them.
  • The Apple Watch Series 6 would also have to be updated to the latest version of watchOS.
  • Finally, the blood oxygen app is only available for users above the age of 18. So, if you are above 18 but are still not able to access the app, then you’d have to login to the Health profile and make changes to your date of birth and current age.

Note: It’s important to note that if your Apple Watch has the Family setup enabled then you would not be able to download or use the blood oxygen app. You will need to disable the Family network if you want to measure your blood oxygen levels from your Watch 6. 

Set up the Blood Oxygen App and Enable Background Readings

Here’s how you set up and use the blood oxygen app on your Watch Series 6

  • Start by launching the Health app on your iPhone.
  • Follow the instructions that are displayed on your iPhone if it’s the first time you’re setting up this app. If not then proceed to the Browse tab, tap on Respiratory followed by Blood Oxygen and finally click on Set up Blood Oxygen.
How Does The Apple Watch Measure Blood Oxygen
  • Once you complete the setup, open the application on your Watch and you will be able to record your levels.
  • If you’re unable to find  the blood oxygen app on your Apple Watch, you will need to download it from the App Store on your Watch. 

While setting up your blood oxygen app, you will be able to track your levels even when the app is not open. This method of background reading will enable you to keep an eye on your SpO2 levels throughout the day without laying a finger on the Watch.

At the end of the day, you can access the blood oxygen section of your Health app and view the findings. You will be able to see whether there was a drop in the level and if the levels drop substantially, then the Apple Watch will notify you to seek medical attention.

How do I turn off background measurements in sleep mode and theater mode?

How Does The Apple Watch Measure Blood Oxygen

For those looking to get rid of that bright red light on your wrist especially if you’re going to sleep or in a movie theater then you can do so from within the settings app on your Apple Watch.

Open the app, tap on Blood Oxygen and then turn off the In Sleep Mode and In Theater Mode.

How to Measure Blood Oxygen on the Apple Watch 6?

While this can be done anywhere and at any time, there is a set procedure you will have to follow so that you receive accurate results.

  • Start by making sure that the Watch 6 is firmly in place on your wrist. It doesn’t have to be too tight or too loose, instead make sure that it fits snug and you’re comfortable.
  • Now, open the blood oxygen app on your Apple Watch and sit still with the face of the Watch facing upwards.
  • Tap on the Start icon on the Watch's face and stay still for around 15 seconds till the device has completed measuring the current blood oxygen levels.
How Does The Apple Watch Measure Blood Oxygen
  • Once it has completed reading your levels, tap on done and you will be able to view the current reading on the Watch face.

If you’re wondering about how the blood oxygen measurements are captured in the background, then I’m here to tell you that it’ll only happen when you’re not moving and only if you have enabled background measurements. The frequency of these background readings will vary depending on how active you are during the day. 

You can even record blood oxygen levels with the Series 6 while sleeping, considering you have enabled the Track Sleep with Apple Watch feature.

How to get the best results?

In order for your results to be spot on, there are a couple of things to remember.

  • You will have to rest your arm on a table or on your lap. The wrist and palm have to be positioned on a flat surface and you must stay still until the complete reading has been captured.
How Does The Apple Watch Measure Blood Oxygen
  • The Apple Watch 6 will have to be secure on your wrist and not loose. Whatever you do, make sure that the back case of the Apple Watch sticks onto your wrist.
  • Make sure the wrist bone is not in the way. If it is, move the Watch by around 1-2 inches up your arm and away from the wrist bone.

Stay still while the sensor is working, this is the best way to get accurate results all the time. However, there may be a couple of scenarios where you might not get an accurate result even though you have followed all the instructions.

View your Health information via the Health App

The Health app on your iPhone stores all the recorded data, from steps to sleep count and even BMI information. It even captures and stores your blood oxygen results from the first time you tracked your SpO2 till date. 

How Does The Apple Watch Measure Blood Oxygen

Whether it’s an on-demand reading or if it was captured in the background, everything that was recorded on the Apple Watch will be available to view on your iPhone. 

Once you open the Health app and then tap on Respiratory followed by Blood Oxygen, you will have a page that displays a table with your daily readings. You can use the filter present there to view the measurements based on your elevation, sleep times and even on a monthly/weekly basis.

Factors that can affect the Blood Oxygen reading

As with any device that uses bio-metric sensors, there are quite a few factors that can affect your results. When it comes to the Apple Watch 6, you would be able to get an accurate reading every time and there are some situations where you would not be able to get an accurate reading even though all the conditions are set right.

  • If you have any permanent or temporary changes to your skin, such as tattoos or scarring in the location you’re wearing the Watch. The ink in a tattoo can actually obstruct the light from reaching your blood vessels and you will not get accurate readings from that area.
  • Another factor that can affect the reading is skin perfusion. This varies from person to person and would change depending on the temperature of your surroundings. If it is too hot or too cold, the sensor will not be able to record the correct values.
  • Certain postures, moving around and even balling up your fist will result in inaccurate measurements. 
  • Also, if you happen to have a high blood rate then the sensors won’t work accurately. Those with a heart rate of over 150bpm would not get a clear and precise blood oxygen measurement.


The Apple Watch Series 6 is the only Apple Watch that delivers accurate SpO2 readings in real-time. As explained earlier, it uses a modified optical sensor that is capable of analyzing the color of your blood which in turn determines your exact blood oxygen level.

It's pretty straight-forward and while it's one of the notable features of the Watch 6, it's not recommended to use this feature to gauge your actual health data. Since it uses only a single direction ray of light, the reading will never be accurate as a pulse oxymeter.

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