It’s been a while since I setup my system, but as I recall they are interconnected via the smart hub, and do not need internet at all. When I first configured our system, IOT was probably the topic of an exploratory whitepaper and not yet reliant on internet. But times have changed! Give it a bit more searching; we’ve been happy for quite a long time with the devices. They even have plugs which you can convert dumb devices to a smart HA device—but you’ll have to get them on eBay because they’ve been discontinued:/