When Fitbit launched the Charge 4 fitness band, one of the features we found the most interesting was its ability to estimate users' blood oxygen saturation levels through its SpO2 monitor. Users could only see the data it collects on Fitbit's mobile app as a graph that shows how much their blood oxygen saturation varies throughout the night, though. As 9to5Google has noticed, firmware update 1.100.34 update changes that with a new SpO2 app for the Charge 4 that shows users' SpO2 levels on the fitness band itself.
The changelog for the firmware update includes an entry that says "Your Fitbit device can now estimate your blood oxygen saturation (SpO2) while you sleep." In an FAQ page, the company instructs Charge 4 owners to wear their bands to bed and to swipe up from the clock face to see their "average resting SpO2 level on the SpO2 tile." Further, the company warns that it may take around an hour after they wake up before the tile actually shows their blood oxygen saturation values.
While it's no substitute to getting looked at by a doctor, the sensor could help medical professionals detect signs of conditions like sleep apnea, since it can tell if users aren't getting enough oxygen while they sleep. Fitbit has been equipping select devices with the SpO2 monitor since the Ionic smartwatch launched in 2017, but it didn't activate the sensor until 2020.