A friend of mine is a tech guy. He fix TV's radio's etc for a living.
Anyway, he bought a cheap cell phone with vibration function, and a sim card for a number.
He opened the phone, took all kinda stuff out of it, and connected it to the ON/OFF thing on his motherboard of the PC. Then he soldered it, and fixed some other stuff. CLosed the PC, and with the eye you don't see a thing.
Now when he calls his "pc" it turns ON, when he calls again, it switch OFF
Really funny, and sometimes useful
Andre