Find Your Fitbit Style
The easiest way to verify which Fitbit model you have is to look at the back or side of the device for the model number. It begins with FB and is followed by three digits. For example, Fitbit Sense has a model number FB512 and Fitbit Versa 3 has a model number FB511.
Here is a complete list of major Fitbit devices and their model numbers and release dates, as well as their compatibility with WITHit bands: