Which Apple Watch Has an Oxygen Sensor? A Complete Guide

​Apple Watch Series 6, Series 7, Series 8, Series 9, Apple Watch Ultra, and Ultra 2 all feature a built-in blood oxygen sensor.​​ This feature, first introduced with the Series 6 in 2020, allows users to measure their blood oxygen saturation (SpO2) directly from their wrist, providing valuable insights into their general wellness, fitness, and recovery. It is important to note that this feature is not available on Apple Watch SE models or older versions, and due to a legal dispute, the functionality is disabled on certain models sold in the United States from January 2024 onwards.

What Is the Blood Oxygen Sensor?

The blood oxygen sensor, also known as an SpO2 monitor, is a revolutionary feature that measures the percentage of oxygen carried by your red blood cells from the lungs to the rest of your body. This percentage is known as oxygen saturation. ​Knowing your blood oxygen level can provide insights into your overall wellness, helping you understand how your body is absorbing and circulating oxygen—a key element for your health. Normal blood oxygen levels typically range from 95% to 100%. Slightly lower levels might be observed during sleep or at high altitudes, but consistent readings below 90% may warrant medical attention. This feature is particularly useful for monitoring sleep quality, identifying potential breathing issues, tracking performance during workouts, and recognizing early signs of respiratory stress or illness 1,4.

Apple Watch Models with the Oxygen Sensor

The inclusion of the blood oxygen sensor has become a standard feature on Apple's flagship watches since its debut. Here is a detailed breakdown of the compatible models:

• ​Apple Watch Series 6:​​ This was the first model to introduce the blood oxygen sensor, marking a significant advancement in the health-tracking capabilities of the smartwatch 1,3.
• ​Apple Watch Series 7 & Series 8:​​ These subsequent generations retained the blood oxygen sensor, continuing to offer users the ability to monitor their SpO2 levels alongside other health metrics 1.
• ​Apple Watch Series 9 & Series 10:​​ These latest models also include the sensor hardware. However, due to an ongoing legal dispute with Masimo, ​the Blood Oxygen app is disabled on units sold by Apple in the United States from January 18, 2024. These watches are identified by a model number ending in "LW/A" 2,5.
• ​Apple Watch Ultra & Ultra 2:​​ Designed for extreme conditions and advanced athletics, both Ultra models are equipped with the blood oxygen sensor, offering the most robust tracking capabilities. Like the Series 9 and 10, the Ultra 2 sold in the U.S. has the app disabled 1,8.

It is critical to understand that the Apple Watch SE, in all its generations (2020, 2022, 2023), does not include the necessary hardware for blood oxygen monitoring. Older models like the Series 3, 4, and 5 also lack this sensor as they were released before the technology was introduced 1.

How the Oxygen Sensor Works

The technology behind the sensor is called ​pulse oximetry. The Apple Watch uses a cluster of LEDs integrated into the crystal on the back of the watch. This cluster includes red, green, and infrared lights that shine onto the blood vessels in your wrist. Four photodiodes then measure the amount of light reflected back 1,4,7.

The fundamental principle is that oxygenated blood (hemoglobin bound to oxygen) and deoxygenated blood absorb light differently. Oxygenated blood is brighter red and reflects more red and infrared light. By analyzing the ratio of reflected red and infrared light, the watch's advanced algorithm can estimate the oxygen saturation in your blood, displaying it as a percentage 4.

The Blood Oxygen app operates in two primary modes:

1. ​Manual Readings:​​ You can open the Blood Oxygen app at any time, tap "Start," and remain still for 15 seconds while the watch takes a measurement 1,6.
2. ​Background Monitoring:​​ When enabled and you are inactive, the watch will periodically take measurements throughout the day and night, building a comprehensive trend of your levels over time 1,4.

For the most accurate results, it is essential to wear your Apple Watch snugly but comfortably on the top of your wrist, ensuring the back crystal has complete contact with your skin 6,10.

Accuracy and Limitations

The Apple Watch's blood oxygen sensor is accurate enough for general wellness and fitness tracking. A study comparing the Apple Watch Series 6 to a medical-grade pulse oximeter concluded that it ​​"can reliably detect states of reduced blood oxygen saturation with SpO2 below 90%"​​ 7. However, Apple is clear that this feature is ​not intended for medical use, including self-diagnosis or consultation with a doctor​ 1,4,6.

Several factors can influence the accuracy of a reading:

• ​Movement:​​ Excessive motion during a measurement can lead to inaccurate results.
• ​Skin Perfusion:​​ Low blood flow to the wrist can make it difficult to get a reading.
• ​Environmental Factors:​​ Very cold environments can reduce perfusion.
• ​Tattoos and Skin Pigmentation:​​ Dark ink or pigmentation can absorb the light from the sensors, potentially interfering with measurements 1,4.
• ​Proper Fit:​​ A loose watch band can prevent the sensors from making consistent contact with the skin 1.

The sensor's performance has been validated across a wide range of skin tones. The sensing platform automatically adjusts the LED intensity and photodiode sensitivity to account for different skin tones, ensuring adequate signal resolution for a diverse user base 4.

Regional Availability and Legal Restrictions

The Blood Oxygen app is not available in all countries due to varying local regulations and health approval processes. While it is fully supported in most developed nations like the United States, Canada, Australia, the United Kingdom, Germany, and Japan, it may be restricted or unsupported in other regions such as China, Monaco, and India 1.

The most significant recent development is the legal restriction in the United States. Following a patent infringement dispute with the medical technology company Masimo, Apple is prohibited from selling Apple Watches with an active blood oxygen feature. This has led to the ​software disabling of the Blood Oxygen app on new Apple Watch Series 9, Series 10, and Ultra 2 models sold in the U.S.​​ 2,5,9. If you purchase one of these watches in the U.S., the hardware is present, but the app is non-functional. This restriction is specific to devices sold by Apple in the U.S.; watches purchased elsewhere and used in the U.S. are unaffected. Currently, there is no way for users to reactivate this feature on affected models, and a resolution may not come until the patent expires or a settlement is reached 9.

How to Use the Blood Oxygen App

Using the feature is straightforward if you have a compatible watch in a supported region.

​To set up the app:​​

1. Open the Watch app on your iPhone.
2. Navigate to the "Blood Oxygen" settings.
3. Ensure "Blood Oxygen Measurements" is toggled on.
4. You can also enable or disable measurements in Theater Mode and Sleep Mode from here 6.

​To take a manual reading:​​

1. Ensure your watch is snug on your wrist.
2. Open the Blood Oxygen app on your Apple Watch.
3. Rest your arm on a table or your lap, keeping your wrist flat and the watch screen facing up.
4. Tap "Start" and hold still for the 15-second countdown.
5. Your result (a percentage) will be displayed on screen 1,6.

All your readings, both manual and background, are stored securely in the Health app on your iPhone. You can view trends over time by opening the Health app, tapping "Browse," selecting "Respiratory," and then choosing "Blood Oxygen" 1. This longitudinal data can be incredibly valuable for spotting patterns related to your sleep, altitude exposure, or overall wellness.

Final Thoughts: Is an Apple Watch with SpO2 Worth It?

For individuals keen on gaining deeper insights into their health and wellness, an Apple Watch with a blood oxygen sensor is undoubtedly a valuable tool. It provides a convenient way to track a key metric of your body's efficiency. If you are considering an upgrade, the ​Apple Watch Series 9 (or Series 10 outside the U.S.) offers a great balance of features and price, while the ​Apple Watch Ultra 2 is the top choice for those needing maximum durability and advanced tracking​ for outdoor or intense athletic activities 1.

However, if blood oxygen monitoring is a primary reason for your purchase, you should ​avoid the Apple Watch SE​ as it lacks the sensor entirely. Furthermore, if you are in the United States, be aware that new models purchased directly from Apple will not have this feature enabled unless the legal situation changes. In that case, you may want to consider purchasing an older, unused model like the Series 8 or buying from a market where the feature is active 9. Ultimately, the blood oxygen sensor is a powerful wellness feature that, when used correctly, can help you make more informed decisions about your health.