[gh02t]

Regarding privacy issues, IMO if that's a problem you've screwed up big time. Stuff like lights should only use local control and not be tied into the cloud or at least it should be optional, and any lights should fall back to working like normal dumb lights if they lose contact with the hub.

When it comes to rolling your own devices with an Arduino or similar, this is much harder to do safely and in a code-compliant manner than you would imagine. Making your own sensors is fun and harmless, but making stuff that is hard wired into mains is a bad idea. It's not totally impossible to engineer a properly safe device if you really know what you're doing, but it'll probably end up costing more than a commercial device and won't come with the compliance testing marks.

I agree, however... even though I have a lot of effort sunk into my own home automation setup it's not for everybody and there are plenty of downsides.

[crooked-v]

For commercial systems that will do that, Hue lights work fine on an isolated network, and HomeKit as a broader ecosystem doesn't require an internet connection to work and is explicitly designed to always treat the local hub as the primary controller.