90% of this video is worthless–mostly, a slightly pudgy guy looking around suspiciously, as if someone were following him. There’s also the not-insignificant matter of the Indiana Jones soundtrack.
But at the :48 second mark you do get to see how the interior latch of a secret door works. After the guy pulls the book back (why is it always a book? I notice the Kipling book…that should be enough of a giveaway…how many people read Kipling anymore? Obviously, it’s a 25 cent book he picked up at a used book store), it pulls a string. Let him describe:
I attached a gate latch at the top back of the bookcase, latching into its counterpart inside the doorframe. I used a rubberband to make sure the latch stays down for when the door is closed. A system of two pulleys feeds a string from the latch down through a hole by the secret book.