Is Polar's SpO2 continuous or on demand? On demand — 45 seconds, when you ask
On demand. Polar's user manual for the Vantage V3 is explicit: “You can measure SpO2 conveniently from your wrist whenever you want in just 45 seconds.” It is a spot check you start yourself, not a reading taken continuously through the night. Polar also states the feature “is not intended for any medical use, diagnosis, or treatment”.
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Why the distinction matters
A single daytime SpO2 reading tells you very little. The reason people care about blood oxygen on a wearable is overnight desaturation — dips while you sleep that you cannot feel and would never catch by pressing a button while awake. A spot check and an overnight trace answer completely different questions, and a spec sheet that just says “SpO2 ✓” hides that entirely.
This is the single most common error in wearable comparisons: treating the presence of a sensor as if it were the presence of a metric. A device can carry an SpO2 sensor and only ever read it when you ask.
Which devices read SpO2 overnight, and which spot-check
*Oura* measures it while you sleep. Oura states the reading requires a sleep period longer than three hours and reports Average Blood Oxygen for the night, on Gen3 rings and newer with an active Membership.
*Garmin* lets you choose. The CIRQA and Venu 4 manuals describe a Pulse Ox mode setting with three options: All Day, which measures while you are inactive during the day; During Sleep, which turns on continuous measurements while you sleep; and a manual reading you start yourself. Garmin notes All Day mode decreases battery life. So for a Garmin, “is it continuous?” genuinely depends on what its owner picked.
*Polar* is on demand only, as above. The Polar Loop does not have an SpO2 sensor at all — Polar's own product page lists optical heart rate and an accelerometer, and says SpO2 and skin temperature are not included.
*Samsung* measures blood oxygen during sleep — Samsung states the Galaxy Ring “can track your sleep patterns by measuring your heart rate, blood oxygen, and skin temperature while you're sleeping” — but does not say whether the reading is continuous through the night.
*Withings* is the one to read carefully. The ScanWatch 2 has blood oxygen, but Withings answers its own FAQ with: “SpO2 measurement is a wellness feature and therefore not clinically validated.” That is unusually candid and worth respecting.
What none of them are
None of these is a medical pulse oximeter. Polar says so directly. Withings says so directly. If you have a genuine reason to suspect a breathing problem overnight, a consumer wearable is a prompt to see a doctor, not a substitute for one.
Frequently asked questions
Pedro Thomaz builds Vitra, a desktop app that reads Oura data against your own baseline instead of a population average. He has worn a ring daily for years and reads these same numbers every morning — which is where most of what is written here comes from. Vitra is not a medical device and nothing on this blog is medical advice.
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