The "privacy screen" is a physical polarization filter - basically a fabric you put on your screen however you like. I don't know of any electrical/mechanical

The "privacy screen" is a physical polarization filter - basically a fabric you put on your screen however you like. I don't know of any electrical/mechanical process that could shift the state of fabric to block light at most angles. If you buy a crappy laptop from a couple of years ago, you won't even have to buy a filter to render your screen unreadable from an angle that isn't perpendicular to the screen. :)