Health TechnologyMarch 7, 2026·5 min read
By the CIRRUS Editorial Team — how we write and source this
Pulse oximeters: how they work and their real accuracy limits
A clip-on fingertip device became a household item during the pandemic. Here's what it can and can't reliably tell you.
A pulse oximeter shines two wavelengths of light through a fingertip and measures how much each is absorbed — oxygenated and deoxygenated hemoglobin absorb light differently, and the ratio between the two readings is used to calculate an SpO2 percentage.
Accuracy is generally good in the higher ranges of oxygen saturation but becomes less reliable at lower readings — most consumer devices are validated primarily in the 90–100% range, with wider error margins in the low 80s and below, which is precisely the range where clinical decisions matter most.
Cold fingers, movement, nail polish, and certain skin tones have all been documented in research to affect reading accuracy — a body of research in recent years has specifically found reduced accuracy in patients with darker skin pigmentation across several commonly used device models, an active area of ongoing device recalibration and regulatory attention.
A single concerning reading is best treated as a prompt to re-check under better conditions (warm hand, at rest, still) rather than an immediate diagnosis — but a persistent low reading, especially with symptoms, warrants medical attention regardless of device-level accuracy caveats.
This article is general health information, not medical advice, and doesn’t replace evaluation by your own physician. Talk to a doctor about anything specific to your own diagnosis or treatment.