The quickest way is to open the Fitbit app, tap your profile picture, then your device — the exact model name is listed there. You can also check the engraving on the back casing of the tracker itself. As a visual guide: Charge models have a slim rectangular screen, Versa and Sense models are square smartwatches, and Inspire and Luxe are narrow pill-shaped trackers. Confirming your model first means the band you order clicks straight on.