Before you attempt this, please note that I've only tried this with an LCD monitor. I don't know if it will work with any other type. Also, it may not work with certain LCD monitors. Also, the results may not be as good as the results I got. I recommend doing this project with a monitor that you don't care about losing. The results are amazing. If you are going to try and make your own, there are a few things to keep in mind. First, I would recommed using a monitor that you don't care about. I bought mine from a pawn shop for $20 dollars. Once you remove the polarized layer, you've pretty much made the monitor useless as to normal use.
If you are good with repairs and that sort of thing, I'm sure you could buy a replacement filter to fix the monitor. So basically, just make sure you are ok with modifying whatever monitor you've chosen to use for this project. Once you have your monitor you need to remove the top layer, which is the polarized layer. It helps to remove the plastic frame from the front but it's not 100% necessary. Once you remove the plastic front, use a hobby knife to cut on the edge around the whole monitor. Press hard enough to make the cut but don't press too hard. That's one thing to keep in mind during this whole process is that you can completely destroy the monitor by damaging the actual LCD part of the screen. Once you make the 4 cuts, then pick a corner to start peeling the polarized layer. I used a hobby knife to "dig" under the layer so I could get a big enough piece to grab onto. Now, every monitor is different so you may experience this part a little different than the next person. You want to peel slowly to try and get the biggest pieces possible and also not to put too much force on the screen. This part could take several minutes to get all of the polarized layer off.
Most LCD monitors have an antiglare layer "attached" to the polarized layer and both of those layers are glued to the hard surface of the LCD. So you may see these extra layers as you are removing them. If you're lucky you will be able to remove all 3 layers by just pulling it off. But it's likely that some glue will be left over. It's also possible that you will lift the polarized and antiglare layer but leave most of the glue. If you look closely in my video, you can see a few spots where the contrast is different. These are spots where the glue came off. If there are a lot of glue spots and it bothers you, it is possible to remove the glue by using paint thinner. But you have to be very careful. If you use the paint thinner, apply it to the glue spots and use a piece of plastic to gently scrape it off. Don't press too hard or you will destroy the monitor. Overall, I would recommend to stay away from the paint thinner and just live with the glue spots.
Next you want to grab some glasses. I used a pair of the 3D glasses you get at the cinema. I never throw them in the recycle bin :). Anyway, you can open these glasses up and remove the "lenses". I ordered 2 - 6" X 6" sheets of polarized filters from a popular online science store. I traced the shape of the area where the lenses on the polarized sheets. I cut them out and placed them inside the frames. Before you cut the shape, make sure to note the proper angle of the polarized sheet with the monitor. I had to turn my sheet 45 degrees to get the correct angle. So when I traced the lens shape on the sheet, I turned the sheet 45 degrees and cut them. (In the video the sheet wasnt turned 45 degrees, but that was just a video mistake) So now you're ready for action. If you hook your monitor up to a computer and put on your glasses you should be able to see the screen just as normal. Anyone standing behind you will only be able to see a blank monitor. If you move far to the sides you can see a little bit of a negative image on the screen, but it's still very hard to make out. Anyway, enjoy!