How does a 2-way mirror work?

Question

How is that you see through one side of it and the other side looks like a mirror? I always wanted know how this works.

Answer 1

The reflective layer is thin enough to allow a person on the nonreflective side to be able to see thru it, however, the person on the reflective side can also see thru it, but only if there is light on the nonreflective side of the glass.
That is why the people that are doing the observing are always in a darkened room, and the people being observed are in a room that is brightly lit.

Answer 2

I think you mean "one-way mirror"