Health sensors
What is the SpO2 a smartwatch measures?
SpO2 is blood oxygen saturation: the percentage of hemoglobin that is carrying oxygen. A smartwatch estimates it with lights and an optical sensor on the wrist. It is a wellness reference, not a diagnosis: consumer watches are not medical devices.
How a watch measures it
The sensor shines red and infrared light on the skin and measures how much is reflected back. Blood carrying more oxygen absorbs light differently, and from that difference the watch calculates an estimate.
The reading changes with movement, strap fit, skin temperature and tattoos. For a steadier measurement, stay still and wear the watch snug, slightly above the wrist bone.
What it is for and what it is not
It is useful for watching your own trends: how it varies during sleep or at altitude. It is not for diagnosing or ruling out an illness. With symptoms or a reading that worries you, the right step is to see a health professional and use a medical device.
What to check before you buy
- Treat it as a tracking feature, not a medical device.
- If you want it for sleep, check that it measures automatically at night.
Products with SpO2 in our store
This is how it appears on their spec sheet. Open each one to see all its specifications.
Guides to help you choose
Frequently asked questions
It gives an indicative estimate. It does not have the accuracy of a medical fingertip oximeter and should not be used to make health decisions.