The Oura Ring’s third generation measures blood oxygen, or SpO2, using red and infrared LED sensors that shine light into the wearer’s finger and use the reflections that bounce back to estimate how much oxygen is in the blood. Well oxygenated blood reflects more red light than infrared light, whereas poorly oxygenated blood reflects more infrared light than red light.
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Pulse oximetry is a technique that has long been used in wearable devices from Fitbit, Garmin, Apple, Withings, and others. According to some studies, pulse oximetry is relatively accurate; however, experts warn that it is not a clinical grade. (Oura is quick to point out in a blog post detailing the new SpO2 feature that the metrics provided by the Oura Ring aren’t meant to be used for medical purposes.)
Oura adds two metrics to the Oura Smart Ring’s blood oxygen measurements: Normal blood oxygen levels and breathing patterns, and average blood oxygen estimates the percentage of oxygen in the blood. In contrast, breathing regularity looks for “abnormal” breathing patterns — i.e., drops in blood oxygen levels — during the night or any nap lasting more than three hours.
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By default, average blood oxygen and breathing regularity measurements are enabled. They can be turned off from the Blood Oxygen Sensing settings in the Oura app’s main menu; Oura notes that when the measurements are active, the battery life of the third-generation Oura Ring “may be a bit shorter than usual.”
The introduction of blood oxygen sensing comes after a series of ups and downs for the Oura Ring. When the smart ring first debuted last fall, Oura revealed that unlocking certain features would require a $6-per-month subscription. Customers were irritated because few of these features were available at launch — Oura previewed updated sleep-tracking algorithms and heart rate tracking for workouts, but the release was delayed.