https://techcrunch.com/2022/07/26/the-third-gen-oura-ring-can-now-measure-the-oxygen-levels-in-your-blood/

Oura, the company behind the Oura Ring lineup of wearable devices, today announced that blood oxygen sensing is rolling out to the third-generation Oura Ring. It’s a long time coming — Oura previewed the feature last fall. But Oura, asserting that the wait was worth it, says oxygen sensing will be able to deliver a “more comprehensive assessment of sleep health and physiology” to owners of its newest flagship product.

The third-generation Oura Ring measures blood oxygen, or SpO2, via red and infrared LED sensors that shine light into a wearer’s finger and use the reflections that bounce back to estimate how much oxygen is in the blood. Richly-oxygenated blood reflects more red light than infrared light, while poorly-oxygenated blood tends to reflect more infrared light than red light.