Blood Oxygen (SpO2)

SpO2 stands for "peripheral capillary oxygen saturation" — the percentage of hemoglobin in your blood that is carrying oxygen. Healthy adults at sea level typically read 95–100%.

SpO2 is measured non-invasively using pulse oximetry — a small sensor that shines red and infrared light through the skin and measures how much is absorbed. The standard form factor is a fingertip clip, but modern smart rings, smartwatches, and dedicated continuous-monitoring rings all use the same underlying technique.

Continuous overnight SpO2 tracking is the most useful consumer application. Drops in nighttime SpO2 can indicate sleep apnea, poor sleep quality, or altitude exposure. Single spot measurements are useful for athletes and travelers but less revealing than the overnight trend.