Fitbit confirmed the rollout to Engadget. The devices are using a combination of red and infrared sensors to determine oxygen variation, although the company cautioned that it wasn't a relative figure. You shouldn't see large variations in your sleep if you're healthy, the company said.

This is coming at a good time for Fitbit. Although Spo2 sensors aren't new in wearables, adoption is spreading. Withings' ScanWatch (an Engadget CES award winner, we'd add) treats blood oxygen tracking as a central feature. Google's acquisition of Fitbit could change where you see the technology after this, but it's good to have now if you're determined to glean more health insights.