Over the last few weeks we have been trying to build an "Intranet of Things" smart home. We have replaced many of our light switches with TP Link smart switches, for example. Critically, though, we have every smart device on a firewalled 802.11n network with NO ROUTE to the public Internet. All devices are denied access to their precious cloud.
Manufacturers do not make this easy. TP Link setup just barely works without Internet access, but it does, if you jump through some hoops.
In general, the current state of "smart home" technology is extraordinarily hostile to doing your own stuff. Everything wants internet access, everything wants to store your data in the cloud somewhere, everything wants to treat you like a product. This grand experiment of ours where we try to have a smart home, but control 100% of our own data, is REALLY EYE OPENING.
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko