A lot of responses to this thread focus on how "one can simply not connect the smart appliance to the WiFi" or "you can just disable its WiFi."
It's my experience that such software settings tend to not be respected. A firmware update might "accidentally" enable WiFi. The appliance might automagically connect to open networks.
But is it just me? A poll!
Have you experienced a "smart" appliance changing its network-related settings (WiFi on/off, etc) without your knowledge?