It seems as though overnight everyone’s talking about SpO2, or blood oxygen, measurements

The latest Apple Watch, Withings smartwatch and Fitbit trackers all feature SpO2 readings – weaving this biometric with numerous others, like stress levels and sleep quality, to help users grasp an overview of their health.

Do we all need to care about our blood oxygen levels, though? Probably not. But as with most health-oriented lifestyle changes caused by Covid-19, it probably won’t hurt to know.

Here, we're looking at just what a pulse oximeter is, why it's useful, how it works, and where you can get one.

We'd highly recommend speaking to your health care professional before deciding whether to buy one or if it's right for you.

Apple Watch 6 Pulse Oximeter

What is a pulse oximeter?

Before big tech released blood oxygen readings to the masses via suave gadgetry, it was primarily something you'd expect to see in hospitals and healthcare spaces. 

The pulse oximeter, which has existed in its earliest form since the 1930s, is a small, painless, and non-invasive medical device that clips onto your finger (or toe or earlobe) and uses infrared light to measure blood oxygen levels 

The reading helps healthcare professionals understand how well a patient's blood is transporting oxygefrom the heart through the rest of the body – and if more oxygen is needed. 

Learning how oxygenated your blood is is useful, after all. Those with conditions like Chronic Obstructive Pulmonary Disease (COPD), asthma, or pneumonia will want frequent readings to ensure their oxygen levels remain healthy, and to understand whether medication or treatment is working.

While it's no replacement for a test, an oximeter may also be able to indicate whether you have Covid-19.

How can a pulse oximeter tell you have Covid? 

Typically, blood oxygen levels should stay between 95% to 100%. Let it drop below 92% and you could have hypoxia – which means a lack of oxygen in the blood. 

Given the Covid-19 virus attacks the person’s lungs and causes inflammation and pneumonia, it’s likely to disrupt oxygen flows. In this case, an oximeter can be a useful tool to detect Covid-related hypoxia – even before a patient even starts showing more obvious symptoms, such as a fever or shortness of breath.

This is why the NHS bought 200,000 pulse oximeters last year. The move was a part of a scheme to potentially detect the virus and prevent deterioration in patients at a high risk of developing serious symptoms. This would also help detect “silent hypoxia” or “happy hypoxia”, where patients show no obvious signs of declining oxygen levels. Learn more about the NHS's Covid Oximetry @home scheme

Fitbit Sense Oximeter

Of course, to know whether your blood is lower than usual requires you to know your normal oxygen levels. This is where oxygen monitoring can become useful. 

The NHS's guide to self-isolation advises calling 111 if your "blood oxygen level is 94% or 93% or continues to be lower than your usual reading where your normal oxygen saturation is below 95%". If readings are at 92% or less, the guide urges calling the nearest A&E or 999.

While a lower oxygen level doesn’t necessarily mean it’s Covid, it could indicate other potentially dangerous health complications.

How does an oximeter work? 

The oximeter beams infrared light onto your skin. Oxygenated blood is brighter red than blood that lacks oxygen.

The oximeter basically measures the differences in light absorption. Red vessels will reflect back more red light, while darker red will absorb red light. 

Where to buy an oximeter

The Apple Watch 6, Fitbit Sense, Fitbit Versa 3 and Withings ScanWatch all measure SpO2 levels. See our full guides on the best Apple Watch 6 deals and best Fitbit deals.

Whichever device you buy, it's not a replacement for medical advice and intervention.

You'll also find standalone pulse oximeters on Amazon, though ensure you're buying a medically certified device with a CE rating. 

High street shops like Boots offer the Kinetik Wellbeing Finger Pulse Oximeter for £30. See all options at Boots

Meanwhile, Lloyds Pharmacy has the Aquarius Finger Pulse Oximeter for £29.95. Shop all oximeters at Lloyds Pharmacy.