I've seen a lot of these projects around but they all use red cellophane which I don't have lying around my house so I made one without using it.

Supplies

Plastic wrap

Scissors

Cereal/Snack box

Double sided tape

Black Sharpie marker

Red Sharpie marker

Step 1: Unfold

Unfold the box you've chosen to make the frame for your decoder. It's a lot easier to do the next steps with the box unfolded.

Step 2: Draw the Frame

Draw out the shape you want for the frame for your decoder. It can be any shape you want. Make sure you draw inside the shape so you know where to cut out later. You can use a ruler if you want to make sure your lines are straight or just go by hand like I did.

Step 3: Cut It Out

Cut the shape out of the box then cut out the inside window. I used scissors but if you want to get perfectly straight lines use a ruler and an xacto knife.

Step 4: Make Another Frame

Trace the cut out shape and then repeat the above steps: cut it out from the box and cut out the inside window. Now you’ve got the two frames of the decoder.

Step 5: Securing the Plastic Wrap

Flip one frame over and put double-sided tape around the edges. Making little loops of tape works as well if you don't have double-sided. Then tear a piece of plastic wrap big enough to cover the frame and place it down against the tape. Make sure it’s pulled tight when you do.

Step 6: Sandwich the Plastic Wrap

Do the same with the tape as above to the other frame and then sandwich it on top of the plastic wrap. Now you’ve got a decoder with a lense!

Step 7: Make It Red

Get your red sharpie and color the plastic wrap inside the decoder frame. Permanent marker works best for this, washable marker won’t dry on the plastic wrap. Once you’ve finished coloring give it a few minutes to dry (otherwise you’ll end up with fingerprints like I did). When it’s dry, your decoder is done!

Step 8: Where to Get an Anaglyph

I got the anaglyph in this picture from a really great online project. You can make one and print it out here: Secret Anaglyph Maker

Instructions on how to use the code are written into the code itself. To print your secret message you’ll have to take a screenshot of the multicolored square to the right of the screen and print it off.

Or if you don’t have access to a printer there's a great Instructables project about writing your own secret message by the Oakland Toy Lab here. Check it out they were a great inspiration for this project.