The video below is a demonstration and guide how you can turn an LCD monitor into a spyproof device that only lets you view the contents if you’re wearing special glasses. I think this is a quite cheap way and the level of tinkering required is manageable as well.
What do you think? I hope you find this one interesting. If you enjoy this kind of science and optical experiments, you should make sure to subscribe to their channel as well. Enjoy!
YouTube: Amazing Secret Monitor! (How To)
Photo credit: The feature image is a frame from the embedded video and is owned by brusspup.