Obviously feeling that the Xbox 360's notification system wasn't good enough, Kiwi Andrew F. went and built himself something a little more elaborate: this set of traffic lights.
Basically an Arduino hooked up to the internet, it pings Microsoft's servers every five minutes to see if Andrew's friends are online. If nobody is online, the light is red. If only one friend is online, it's orange. If two or more are online, it's green, and that means it's party time.