One can still conduct deauth attacks fairly easily, or, if the device just picks the strongest open network signal, one can set up a dummy / honeypot WLAN right

One can still conduct deauth attacks fairly easily, or, if the device just picks the strongest open network signal, one can set up a dummy / honeypot WLAN right next to the appliance that has no internet connectivity, and as you note with the basement reference, faraday solutions can work well, too, not to mention simply removing or disabling the networking hardware. This is also true for cars - it's often not terribly difficult to pull the fuse for the cellular modem provided you can procure a manual.