Home Science COVID-19: Why Pulse Oximeters Are Superior to SPO2 Smartwatches

COVID-19: Why Pulse Oximeters Are Superior to SPO2 Smartwatches


Covid-19 seems to have latched onto humankind and keeps on making a comeback in the form of different variants. Keeping a close check on your blood oxygen levels is still one of the best precautionary measures you can take amidst infection risks. 

Pulse oximeters have always been the go-to method for monitoring your SPO2 levels, but many people rely on their latest smartwatches to get that data. A lot of smartwatches have small SPO2 sensors and claim to offer similar levels of accuracy along with many other fitness features.

But are smartwatches as good as a good old pulse oximeter when it comes to monitoring your blood oxygen levels? We don’t think so, and this article will tell you why.

Pulse Oximeters Are More Accurate

While the latest fitness bands with SPO2 sensors can do a similar job as a nonin pulse oximeter, the results might not always be as accurate. Taking several readings on both devices reveals variations in terms of accuracy, but the pulse oximeter remains more stable and consistent in its readings.

The differences in readings typically stem from the different ways in which a fitness band and a pulse oximeter measure your SPO2 levels. Pulse oximeters use transmittance oximetry whereas smartwatches use reflectance oximetry. Let’s look at the two ways in further detail. 

What Are Reflectance and Transmittance Oximetry Methods?

Reflectance and transmittance oximetry are the two most commonly used non-invasive methods for measuring a person’s blood oxygen saturation level. Both of them involve the use of a photodetector and light sources (red light and infrared). However, the two versions of oximetry mainly differ in component positioning. 

Transmittance Oximetry

Transmittance oximetry involves positioning the photodetector and light sources opposite to each other, while your index finger (or the ear lobe, or any other site being tested) remains in the center. As light passes through your fingertip, the photodetector positioned at the other end gets an accurate and stable SPO2 reading by measuring the light that passed through your fingertip. 

Due to the positioning of the components in transmittance oximetry, it’s highly effective in the care of thinner measurement sites such as your finger.

Reflectance Oximetry 

Reflectance oximetry involves positioning the photodetector and light sources on the same side. The diode on the photodetector captures the reflected light that bounces off of your target site (i.e. your wrist — in the case of a fitness band) and returns an SPO2 reading. Since this method of measuring your blood oxygen levels doesn’t require a thin measurement site, it’s commonly used in fitness wristbands.

Objectively, transmittance oximetry is seen to be the more accurate measurement method for blood oxygen saturation levels. However, it’s impossible to implement it into the form factor of a smartwatch, so pulse oximeters are naturally more accurate than them.


Pulse oximeters are more accurate than smartwatches due to many reasons. Not only do they use the more precise measurement method, but also have dual sensors (not all smartwatches have them). Pulse oximeters are also equipped to compensate for external factors that can disturb the reading. These include the size of your finger, ambient light, and the light that gets absorbed by finger tissue.  

With that said, if you don’t have access to a pulse oximeter and need to take an SPO2 reading immediately, feel free to rely on your smartwatch in a pinch as they’re also sufficiently accurate for occasional use.