What is SpO2? How it works in Smart Watches? Why it is important?

SpO2 also known as Oxygen Saturation, is a measure of the amount of oxygen-carrying hemoglobin in the blood relative to hemoglobin not carrying the oxygen.

Several smartphone brands have recently jumped into the fitness tracker segment and launched smartwatches with highly promising features, and one of the features is SpO2 or Blood Oxygen Saturation.

The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal arterial blood oxygen saturation levels in humans are 95-100 percent.

What is SpO2?

In simple words, the SpO2 sensor is capable of measuring your blood oxygen level. The human body needs oxygen to survive, which means that higher SpO2 levels are good for us.

If you have lower levels of SpO2 means, you have symptoms of Hypoxemia. According to the reports, 95-99 percent is a normal reading for SpO2.


Why Track Blood Oxygen Saturation?

An oxygen saturation percentage of more than 95% is considered to be a normal reading. If you see a score of 92% or less, then it could be time to further investigate, and find out whether it’s related to an as yet undetected health issue.

It can be used to check their breathing via a ventilator, measure a person’s ability to handle intensive physical activities, and it can also check whether they are experiencing breathing issues when sleeping.

SpO2 LevelIndicationHealth Care Intervention
Normal in Healthy IndividualsMore than or equal to 95%No significant intervention needed
Normal in people with COPD (Chronic Obstructive Pulmonary Disease)88% to 92%Continue with Respiratory assessment and monitoring
Hypoxic85% to 94%Assess for underlying respiratory diseases and initiate oxygen therapy, especially in COPD patients.
Severely Hypoxic Less than 85%Administer Supplement Oxygen Immediately

However, it’s sleep apnea that really makes SpO2 a worthwhile sensor. Sleep Apnea is a disorder that could lead to an increase in the risk of high blood pressure, and can even cause a heart attack. And that’s where many health watches and wearables can come in useful.

It can also be a valuable piece of health data for people suffering from a range of conditions including asthma, pneumonia, heart failure, and lung cancer.

How does the Smart Watch Measures SpO2 levels?

Fitness trackers are capable of measuring SpO2 levels in a similar way to how a heart-rate monitor works. The device uses a highly sensitive photodetector that is capable of seeing the hemoglobin in the user’s blood vessels.


Smart Watches uses the reflectance pulse oximetry technique to measure SpO2 levels.

In simple words, the device projects the infrared and red light to the user’s body surface and the light reflected from the subcutaneous tissue to the sensor. The blood oxygen level is determined between the release and reflection of light.

What is SpO2?

However, do note that this is accurate to a certain level; that’s the only reason manufacturers claim that their devices should not be used for medical diagnosis.

Why are SpO2 Levels Important for Users?

We know that the higher SpO2 levels are important for all the users, but it matters widely for two types of users – Athletes and people with health conditions.

Athletes keep an eye on SpO2 levels because while training, their body needs more oxygen, and the demand for oxygen impacts their training sessions.

People who take altitude training need to monitor their SpO2 levels because it’s difficult for them to extract the exact amount of oxygen in high or low altitudes.

SpO2 monitor will be a great help for people having medical conditions like sleep apnea. It is a condition where people wake up at irregular intervals during the night due to difficulty in breathing.

Smartwatches with this feature can monitor the movement during sleep and can alert users about the problem to take necessary action.

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