This will be a good idea to hide stuff in.
Step 1: Use About 4 to 5 Books
Cut the first book in a Band Saw, if you have one. After you cut it, try to glue all the pages together.
Cut the second book and glue it together to the first book.
Glue all three of them together.
Now glue all the books together and let the glue dry for a little bit.
Take some pieces of woods. Measures the book and the sides.
Glue the pieces of wood On the books.
Last step, take a little pieces of wood and place it at the bottom of the book.
Step 9: Arduino
Mimic this set up you should have a 4.7 resistor (yellow violet Red) 8 ohm speaker and a photo sensor. You can get the code from this link( www.arduino.cc/en/Tutorial/Tone2)
Put the Arduino in the books