Blood Oxygen (SpO2) Monitoring on Apple Watch, Galaxy Watch, and Fitbit

Blood oxygen level — also called SpO2 — is a measure of how much oxygen your red blood cells are carrying. Hospitals measure it with a finger clip device called a pulse oximeter. Many modern smartwatches now include the same technology built into the watch itself.

Normal blood oxygen levels for healthy adults are between 95% and 100%. A reading between 92% and 94% is considered borderline and warrants attention. Anything below 90% is generally considered a medical concern that should prompt immediate contact with a healthcare provider.

The SpO2 sensor in a smartwatch works by shining light through your skin and measuring how much light is absorbed — red blood cells carrying oxygen absorb light differently than those without it. It is a reliable indicator when measured correctly, but consumer smartwatches are not as accurate as clinical pulse oximeters and can be thrown off by poor fit, movement, or cold hands.

Apple Watch Series 6 and newer, Samsung Galaxy Watch 4 and newer, Fitbit Sense, Charge 5 and newer, Garmin Venu, and many other devices include SpO2 monitoring. Each has a dedicated app for spot checks and a background monitoring mode that records overnight oxygen levels — useful for detecting potential sleep apnea patterns.

During COVID-19, blood oxygen monitoring became much more widely known because a drop in SpO2 is an early warning sign of respiratory complications. People with asthma, COPD, heart disease, or sleep apnea have particular reason to monitor this metric regularly.

Quick Tip: For an accurate reading, sit still in a warm room. Cold hands and movement both reduce accuracy significantly. Take three readings two minutes apart and average them.

Important disclaimer: Smartwatch SpO2 readings are not medical-grade and should not be used for medical diagnosis or treatment decisions. A clinical pulse oximeter provides a more accurate reading. If you are experiencing difficulty breathing, chest pain, or persistent SpO2 readings below 92%, seek medical attention immediately. Do not rely solely on a consumer device for health decisions.