I’ve used Home Assistant on a Pi 3B+ for about a year now. My main objective is like yours, I want as few devices as possible connected to the internet and generally only buy devices that have a local API (local polling in HA terms). I do pay for Nabu Casa, HA’s cloud service for convenient access to everything but nothing I use requires it. This also help support a project that I really enjoy using and rely on.
I have most devices connected to an old wireless router that is completely disconnected from the internet. The raspberry pi is connected to my main network through ethernet and is connected to my “smart network” over wifi. I like to think of the HA instance as a two way mirror since it can reach the internet and see the devices but the devices themselves can’t phone home or access the internet in anyway.
For bulbs, light switches, and smart plugs I generally stick with TP-Link Kasa. The local API works great with HA though I believe they are removing this in future firmware updates [0]. This appears to be for the UK only but I’m not 100% sure on that. I purchased a plug a few months ago that still works.
My thermostat is a Venstar color touch with the local API. I have it connected to the internet but I could disconnect it and everything would still work how I want.
You can flash Wyze v2 cameras with the official RTSP firmware to view them locally. You lose some of the features of the Wyze cams but I think this is a fine trade off. While this works with the Pi, streaming video taxes it a lot. It isn’t a perfect experience by any means.
I also use Zigbee devices instead of Z-Wave (no real reason other than the first device I wanted was Zigbee). I have a Sonoff Zigbee bridge flashed with Tasmota that allows me to use any compliant (or quasi compliant in the case of Xiaomi Aqara) plug, motion sensor, temp sensor, etc across brands. The Zigbee bridge is also has access to the internet because it needs to connect to an NTP server. This means that these devices work fine when the internet goes out but if for some reason the hub gets power cycled while having an internet outage they stop working.
You can get Zigbee antennas that connect directly to the Pi but I avoided this because the USB ports can cause interference. You can fix this by getting a USB cable extender.
Feel free to ask any other questions about my setup.
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