Unless something has changed, Fitbits are one of the few BT devices that do not spoof and rotate their advertised MAC. As a result, they are very well suited for use with reelyActive which can be a nice complement or alternative to FIND.
You can set a static IP on the phone itself though. It’s probably not a best practice but I’ve done that in a pinch in the past. On Android you can do it from the Advanced settings for the wifi AP config (i.e. long press on the ssid and press “Modify” and then you will have an “Advanced” option which will open up the fields where you can enter your IP/NetMask, etc.).
Is this able to distinguish between speaking to your local Alexa/Google Home in the house verses the apps running on your phone?
Probably wouldn’t work for us dog owners. 
Probably wouldn’t work for large breed dog owners. 
Great writeup! Thanks for contributing!