Fitbit users were surprised with an added feature on their wearable this week — the ability to check the variability of oxygen levels in their bloodstream. 

Users with any of Fitbit’s Sp02-enabled devices can now access an Estimated Oxygen Variation graph. The Sp2 devices include the Charge 3, Ionic, Versa, Versa Lite and Versa 2, according to Fitbit officials. 

The update, which was confirmed to MobiHealthNews by a spokesperson, works by combining data from the red and infrared sensors on the back of the device, according to the company. 

WHY IT MATTERS 

Blood oxygen variability levels can help detect a number of conditions including sleep apnea, a fairly common condition in the US. According to the National Sleep Foundation, more than 18 million people have sleep apnea, impacting between 5% and 10% of the population. 

Individuals with the condition are at a higher risk for high blood pressure or heart problems, Type 2 diabetes and daytime fatigue. 

THE LARGER TREND 

Fitbit isn’t the only wearable looking at Sp02 capabilities. Last week at CES French wearable company Withings unveiled its new ScanWatch, which includes an ECG and Sp02 sensors. 

Unlike Apple, which has continued to shy away from built-in sleep monitoring features, both Fitbit and Withings have sleep-focused programs on their wearables. Both, it is important to note, also have a longer battery life than the Apple Watch. This has opened the door for tracking tools like the Sp02.