Like the other commenter said, smart switches are the way to go. I prefer the Shelly modules behind light switches. They are tiny, affordable and their new generation does Zigbee/Wifi/Matter/Bluetooth, so always something that suits your installation.
Agree with your Shelly-behind-the-switch model. My one hesitation going all-in with them has been perhaps reaching an eventual state of "too much 2.4Ghz WiFi traffic on a narrow IoT-specific WiFi network", but I suppose that's easily solvable by buying another AP. Currently I'm happily running a few of them behind the wall plate in my switches (check the space in your switch box first!)...no issues after many many months of continuous operation. Didn't know about the new gen supporting Matter, that's great.
Also, I too wanted to extend to you a really big THANK YOU from a very happy member of the HASS community. I came over from OpenHAB a handful of years ago and I couldn't be happier. Please keep up the good work! Good luck with all the hardware sales and Nabu Casa stuff!
In real terms though, it not that bad. I've got about 25 such devices always online and the traffic really is negligible. Most devices aren't sending anything while nothing is happening except for the periodic heartbeat like once a minute. Its not noticeable, even on my 20MHz wide network.
I have like 54 devices running on 3 unifi APs...it's unnoticeable (either that or my phone/laptop etc. are just using 5ghz and happy about it - either way).
I use smart lights with smart switches in detached mode and they are not resilient to ha going down. I wish I could get smart bulb functionality (dimming, color change) with smart switches being the physical driver of them being on/off.
I’ve got some inovelli white series switches that are on a circuit with Nanoleaf thread based lights.
I’ve managed to bind them using Matter bindings, so even if HA is offline, the switches can still on/off and dim the bulbs.
No UI supports this yet (though I think HA is working towards it), but the underlying protocol support exists, and products are starting to come to market that take advantage of it.
I think it 2-4 years, it’ll probably be ironed out and working well, but if you really want it, you can have that now with matter/thread.
I think Zigbee devices also have bindings, and those should probably be a lot more mature, but I haven’t played with those yet.
Not sure about color change, but dimming works fine - I have Shelly Dimmer2 modules behind switches, paired with "dumb" dimmable bulbs. Remotely controlled by HA / Adaptive Lighting, while also working with physical switch.
One solution to this if you're using Shellies to provide your "turn a dumb light switch into a smart light switch" is the scripting it has on offer.
I have 100% Zigbee lights, and each lighting circuit has a Shelly Plus 1 with the relay in "detached" mode (so the shelly will sense the light switch changing from open to closed and send a command to HA to turn on the lights via Zigbee). Most (all?) smart bulbs have a setting for "what do I do when power is restored" and you can set it so that they come on when power is restored.
You can then create a script that uses the MQTT HomeAssistant up/down topic and if HA is down, when the switch changes position operate the relay.
It's not perfect - if you have a powercut during the night all of your lights will come on when power is restored.
I totally missed Shelly becoming an HA Darling - I have an older home with some of the wiring not having a Neutral wire, so Lutron Casetta has been my only option and those No-neutral dimmers are extremely expensive.
