> What is the resolution? Can I track my cat through the house? See when they go to the feeder? Count my own bathroom visits?

None of the above.

The setup process has you select 3 reference devices. You should pick the devices so that your normal motion areas are between the device and the router.

The router then watches the WiFi signals from those devices. If they fluctuate more than baseline, it's assumed that something is moving around in the area.

It's a threshold detection that can serve as a crude motion sensor for home/away purposes.