Hello I am new on this community.
I need some advice for hardware that would connect to HomeAssistant without needing Internet connection. So basically, HomeAssistant should be able to speak locally with all the devices in the local LAN.
I want to be able to monitor circuit voltage/currents, trigger 120/240 switches, monitor some water flow sensors, temperature sensors.
If anyone has suggestions of brands to look for, I would appreciate.
All ESPHome programed devices are connected locally to HA. So, either use ESP8266 or ESP32 and build from scratch or buy some ready-made modules and change FW (sonoff…anything that uses esp chip)
Thanks I will look into it.
Tasmota also should be local, and doesn’t need a hub for light and switch groups. So if HA goes down, the lights should still work.
Correct, tasmota is also an option. The main difference for end user between two is that esphome is fully programmable and a bit hard for beginner, while tasmota is loaded pretty much configured. But there is also a down side: you can program pretty much anything on esphome, while tasmota is limited here.
And, esphome also can work locally, if programmed so.
When you setup HA, depending on which version, think about ssl and local/remote as well. I had mine only accessible via remote (duckdns) and this posed issues with internal devices esp. for casting.
Now I have HA via a reverse proxy and HA is now internal as well as external available.
Added to that, I used zigbee2mqtt with sonoff and innr devices, not needing internet. Philips HUE…same.
For the two (imho) annoying tuya-wifi switches, even when integrated via tuyalocal, not sure if that works (and not trying that out 
)
You could go with ZigBee.
https://www.home-assistant.io/integrations/zha/
Or,
https://www.zigbee2mqtt.io/supported-devices/
Plenty of devices you can control/monitor locally.
I see it a lot but in my case, this deployment is for my chalet and there are 6 houses to connect. They already have wifi but if I go with zigbee, I will need some kind of hub in every building, duplicating the wifi network.
I was planning to add all IoT on separate vlan only accessible by HA. My HA instance is already accessible internally and externally using https with my domain name so I sould be the only one, through HA to be able to control my devices.
I bought different hardware from Shelly, they seem great and totally local, at least once configured which I don’t mind. I also pulled out eWeLink 30A relay switch that I could never connect before but this time with little more know how, I connected them to eWeLink and then locally using an integration from HACS.
One of the next topic will be cameras that can be locally controlled, not too expensive, wifi or PoE…
I have hooked up an MQTT to my HA but I still have not figured out what it does and if I need to configure it somehow. I read that I might need to set retention policy so that the state of my switches is good when starting HA because now they are disabled until I flick it form outside HA. I need to read more about this…
So many possibilities I am really excited but my final goal is really an IoT isolated network only connected to HA.
Well good luck with that my friend. Enough for me with only one house 
Kindly share how you go with it, and maybe how you achieved this in-the-end.
Take care 