I remember when I rented a palace in Singapore, my landlord asked me to download an app called MyKNX to control the lights and blinds in the room. I dumped some packets, and found system is using tcp/ip and the KNX is standardized protocol.

The box is more like a PLC than “smart things”, so it doesn’t need internet to function.

It’s also supported by home-assistant. I want to get one when I’m building my own home.

Edit: added something details