This will show you how to make a secret compartment that can be built into a bookcase, or some other piece of furniture. It uses a sneaky lock that doesn't expose any hardware to the surface. If you can keep from showing all your friends (I couldn't), this would actually be a useful place to store valuables. This design is very flexible to all sorts of shapes and sizes. It can also be installed vertically.

You will need:

A bookcase. I built my own, but virtually any sort of furniture will work: bookcases, china cabinets, dressers, whatever. Just be sure there is a clear amount of space underneath, and the surface for the hatch is at least half an inch thick.
Magnetic Child Lock
Concealed Hinges

I know these pieces can be found at most hardware or home improvement stores as well.

UPDATE 1/9/08:

WOW! Thank you so much to everyone who has commented and checked out my instructable! I had no idea people would find it this interesting! Keep experimenting and sending me your thoughts and variations on my design!

Also, Cousin Eddie wanted to see if neodymium magnets could open the lock, instead of the key, here are his findings:

"Anyway I checked to see if I could open a latch with simple neodymium magnets & found that it took at least 3 small (watch battery size) neod. magnets to open it. BUT you have to have the polarities of all the magnets (including the one inside the latch) lighted up.... otherwise it wont work. Simple to do though. Think I will mount the magnets in my own "key". "

Thanks for the findings!

UPDATE 1/27/08:

I received a request for some pictures of what my bookcase looked like as a whole. I put it them in at the end.

Step 1: Cut Out the Hatch...

Use a hand-held jig saw to cut out your hatch. I was able to remove the shelf during this step, which makes this much easier. For best concealment, cut along a joint, (ex: in the corner) so the cut looks as natural as possible. For this example, I didn't, but the outline is still faint. Use as narrow a blade as you can, as any gap would look really obvious. This is where you are free to adapt the size and shape of the your hatch.

Step 2: Install the Hinges...

This is pretty simple, although drilling holes for the hinges into the surrounding shelf can be tricky with smaller hatches unless you have a right-angle drill. With these hinges, I had to chisel the hatch and counter-sink the hole, in order for the the hatch to fit flush with the shelf. For the fitting the hinge to the hatch, I used my trusty jig saw and a chisel until the hinge fit flush with the rest of the wood.

Check the movement of the hinges, and adjust them if need be. Ideally, the hatch should still be flush with the shelf.

Install a small block opposite the hinges, to keep the hatch from falling into the compartment below.

Step 3: The Fun Part...

Install the magnet lock per the manufacturers directions. Ensure the lock creates a tight latch. For my hatch, I had to shim the other side of lock to make a tight fit. The pictures below describe how this lock works.

Step 4: Build a Box Below and Complete...

Next build a box underneath your hatch. Again, the dimensions of this are up to you. Don't make the box too much bigger than the hatch though, as this will make it hard to reach around in.

Here is a photo review of the entire method of opening the compartment: