The Light Blue Bean built by Punch Through Design is a versatile Arduino device with Bluetooth Low Energy (BLE) built in. The Bean’s default 3v battery could typically last a month when running a minimal sketch. A door bell button is possibly the simplest arduino device you could possibly build. A press of the button would notify an android device through BLE that someone is at the door. This post will provide an idea on how this could be built using minimal power (on the Bean) and minimal code.