This application will not display connected devices. Ensure the device you need to detect is not connected. A minority of devices must be in discovery mode before they are detected, like some BT Headsets.
It will display the signal strength in dBm of all non connected Bluetooth devices it picks up. A list of devices with their Bluetooth names and MAC addresses will be displayed with a signal strength meter for each. You can use this to find your missing FitBit or other Bluetooth device. You can also use it to debug Bluetooth connectivity problems.
Signal updates can take up to 15 seconds to one minute on some devices. Please be patient when you use this application. Depending on various factors, a minority of Bluetooth devices will not be detected at all by this application. This is mostly out of the control of the developer unless Android is changed in this field. Please consider other people when you rate this application. For most people it works. But if it gets to many low ratings it must be removed in order to keep the developer name high with other apps. And then no-one gets anything.
So here is the deal. Rate this app low and I will remove this app and next time you will have nothing to try.