Here's The Science Behind How A Two-Way Mirror Works
Mar 7, 2015
As this video explains, this is done by changing the reflective surface behind the glass and then creating an imbalance in lighting between the two rooms. This actually happens on a smaller level every day. If you have the lights on at night, you'll notice it's hard to see outside and your windows are closer to being mirrors. Two-way mirrors are based on the same idea, with a little extra help.
If you've ever watched any show or movie that had anything to do with police investigations, chances are you're already familiar with the concept of a two-way mirror. It looks like an ordinary mirror from one side, but works like a window on the other side to allow for secret observation of someone.