Need remote access to your computer once in a while, but don’t want to leave it on and wasting power the rest of the time? Then you might want to check out this Remote PC Startup System by MAKE subscriber Blake Foster. He used an Arduino, Ethernet shield, and homebrew relay board to add a internet-enabled switch to be able to turn his computer on from anywhere he has Internet connection. He estimates that the savings on his power bill will pay for the hardware cost in about 3 months.
Remote control for a personal computer