I have worked with home automation for more than 20 years. My first project was very simple; I wantet to be able to turn on heating in my vacation house before I left home.
This was achived with a small single chip webserver pulling a relay which switched on the circulaton og hot water from the heating unit to the radiators in the house.
This became mor and more advanced as I realized the need for being able to verify the amount of heating oil in the tank. I implementet a one-wire network with an aproximity-sensor to establish the distance to the surface of the oil in the tank. Based on this, and the profile of the tank, I could calculate the remaining volume og oil.
I implementeted an OpenHAB server and many more sensores and controles were added.