This instructable shows the principles involved in making devices to control home automation over the internet. We're going to construct a device (or several of them), that talk to each other over the internet to control lights, motors for curtains/blinds, power sockets etc.
In contrast to devices controlled from a web browser or phone, these are designed to be simple, Arduino based devices that are capable of talking to each other bi-directionally. They may be in the same house or in different buildings and may have one way communication (e.g. a light switch and light) or two way (e.g. an automation controller).
It's possible to have local Device/Relay combinations to control Mains socket power to TVs, Computers etc..
Also you could see this working in building control. Commercial examples that work over local or proprietary interfaces are : Clipsal C-Bus, X10, Bus-SCS.
The Picture shows an example of what we're trying to achieve using the commercial C-Bus devices as an example.
(http://en.wikipedia.org/wiki/File:CBus_Wiring.gif). But in our case the C-Bus is replaced by the Internet or a Local Network.
Practically speaking, it would make most sense to have one device per room with several switches, sensors and possibly low-voltage motors wired into it, and one device at the distribution board controlling relays or dimmers.
A major factor in Energy Waste is having Lights on too brightly during periods when a room is adequately lit from Natural Light. Adding a Light Sensor Device in a Room with a Dimmable Light Device significantly increases Energy Efficiency by controlling the Room Light in response to the sensed light in the room.
By the way. If you like this Instructable, you might also like to read My Blog covering various projects and Tutorials