Sometimes, we may put the phone in bedroom, and we will not know someone is calling. With the bluetooth connectivity, it can communicate with your Android phone at least 10 meters or above. You can put the lamp near your TV or anywhere you stay. Also, you can use Android as a remote control to turn on/off the lamp (or any devices).
Hareware: AVRtiny2313, Bluetooth module, lamp

Ready to go:

Video Demo: