How to enable the SpO2 monitor on your Fitbit | iMore
Amazon.com: Fitbit Versa 3 Health & Fitness Smartwatch W/ Bluetooth Calls/Texts, Fast Charging, GPS, Heart Rate SpO2, 6+ Days Battery (S & L Bands, 90 Day Premium Included) International Version (Pink/Gold) :
Fitbit Charge 3 review
Fitbit is unlocking the dormant SpO2 sensor in five wearables
Fitbit's Charge 4 band can now display blood oxygen saturation levels | Engadget