How does a two-way mirror work?
There are gaps in the metallic coating, tiny ones. Kind of like mixing a screen door and a mirror. A two-way mirror really is visible either way. If both sides of the mirror are equally bright, you will be able to see yourself and the other side, but if one side is bright and one side is dim, then the person on the bright side will only see themself and the person on the dark side will see through like a window.