Your washing machine could be sending 3.7 GB of data a day — LG washing machine owner disconnected his device from Wi-Fi after noticing excessive outgoing daily data traffic
Just put the device on a separate wifi without internet access, or look at the "child protection" features of your router. Ours can put devices based on their MAC into "access groups" which range from "full access" over "internet from \ to " to "no internet at all".
Kind of wild we're getting to the point where various pieces of equipment, with hardware we don't want to use, need to be tricked into connecting to a fake network in order to prevent themselves from publishing their credentials.
And that's if we assume there aren't open Wi-Fi networks they won't connect to automatically, in order to do their dirty deeds undeterred by their pesky owners.
Luckily, most embedded devices lack the smart to attach to two networks at the same time. So you keep it locked into a network where it can only do your bidding, and it won't listen to anyone else. Unless they built in some very crazy and nefarious code and drive around with network enabled cars in the owners neighborhood.
Wait, I don't need a tin foil hat for this... It was national news
At the point it becomes impossible to buy hardware that doesn't have a Wi-Fi antenna in it, I'll get really worried regardless. Tricking a device into connecting to the right wifi network already is so wild, and people shouldn't have to do that. I'm smart enough to. Not everybody is. Not everybody has the money for an extra router.
No need for an extra router. I just put those device into the "has no internet access" group. It is one of those "Parental Control" things. Every device inside the net can see and talk to it, but itself cannot talk to anything outside.
Which is understandable... To me, anyway. Until the router needs to be reset, or something else happens to it.
Come to think of it, I'm not sure if my router hardware actually supports this possibility. I've got a PiHole, but I'm also not the average person I play telephone tech support for.