GoKawiilFitbit Air sensor can be worn under standard watch straps, users show
Fitbit's Air tracker can be combined with a traditional watch using its 18mm Performance Loop band threaded under the watch's spring bars, with the watch sitting atop the wrist and the tracker underneath. Lug widths of 18-20mm generally work, while 3D-printed adapters let owners keep their original straps and mount the removable sensor beneath them instead.