QR code reading with camera - Android

I am currently researching to build an alarm clock application in Android. I am utterly and completely new to programming with QR codes. I know nothing about it. But right now, I want to find out the feasibility of creating an application with QR code functionality. (I have two weeks to build this) My first question is: would I have to handle the camera myself in the code i.e. do I have to fire it up and then close it and then process the QR image? 2nd Q: How would I create the QR code and then when I scan it, how does it know it scanned the right one? I want to print one, place it in the kitchen or bathroom and then when the alarm goes off, I have to scan the code before the alarm turns off.