Your Fitibit smartwatch can now do what the Apple Watch can't: monitor blood oxygen saturation.

The new feature was launched without much fanfare, but TizenHelp noted today (January 15) that some Fitbit owners have noticed blood oxygen saturation data being displayed within the Fitbit app's graph.

Many Fitbit smartwatches have had the ability to monitor blood oxygen levels for some time, starting with the Fitbit Iconic in 2017; the Iconic had an SpO2 sensor, but Fitbit had other wearables with that sensor had shipped, but had not yet enabled the feature. That has obviously changed thanks to software updates that have been rolled out to these watches.

In addition to the Iconic, the Versa, Versa Lite, Versa 2, and Charge 3 all support the new tracking feature.

Fitbit's blood oxygen saturation data is only an estimate, but even that can help track health. Large fluctuations in blood oxygen can point to breathing problems and provide clues that a person may be suffering from conditions such as sleep apnea.

Rumors about the Apple Watch have long suggested that Apple's smartwatch will eventually add sleep tracking capabilities, including sleep apnea detection, and Apple holds several patents in this area. And while this feature could be the focus of this year's annual watchOS update, Fitbit is ahead of Apple.

Another smartwatch with health-tracking ambitions, Withings' $249 ScanWatch, debuted at CES earlier this month. Pending U.S. Food and Drug Administration (FDA) approval, that device also includes, among other features, an SpO2 sensor to measure blood oxygen saturation. However, while Withings awaits the FDA's OK, the ScanWatch does not yet have a ship date.