I also used this to find a lost fitbit! It took 5 min, and it was in tall grass.
To the next person that lost their fitbit: -40 dBl means that you are just a few inches away from the fitbit, -99 dBl you are about 20 feet ( no walls )
To the app designer: you should make this with a signal strength bar and gear the GUI as a locator, then sell it for a buck as a Fitbit finder. I will of accept a customary 20% idea fee or 1million dollars which ever is higher.
Hunting Poodles about Bluetooth Smart Scanner