I have my old flat in 2000(ish) fully linked. This. Included PIR sensors, door sensors, and lamps, lights. I also had. The heating fitted with an x10 switch. This meant that I could turn the heating on and my kettle on remotely on the way home from work.

X10 was nice that it could communicate through main, but when I started to use Ethernet over power, it stopped working. It also was one-way. There was no confirm or status from the switch devices.