I just finished the hardware assembly and the arduino code. I am know able to published the measured value via Bluetooth Low Energy. I checked the system using "nRF Connect" application. That was the easy part.

Know I need to create an android application ( this is my first time!). I managed to found an open source alarm clock that may fit my needs: https://github.com/SheldonNeilson/Android-Alarm-Clock

But I am still hesitating to start from scratch...