I'm sure you have all heard of the trick in movies, where someone goes into a hidden room , which can only be opened by pulling out the correct book from a bookshelf.

Watch a quick video of it in action , turn up your speakers to hear the buzzer

I decided to change this movie cliche a bit. I took a sharp IR sensor and mounted on a bookshelf. It measured the distance to any book that was pulled out, and checked to see if that was the "key" book. After getting it to work with one book pulled out. I made it a combination of books. It has to be 7-9-5 in that order, any other books are ignored. It resets after 15 seconds. I made a video and it is currently processing on YouTube so i'll post it here , once its done processing( probably when I wake up it will be done)

Right now the code to activate a buzzer.
Pull book 7 out
push 7 in
pull 9 out
push 9 in
pull out 5
KEY SOLVED- buzzer rings