One-way mirror

One-way mirrors for upper-level observation deck viewing down into a classroom (University of Wisconsin-Eau Claire)

A one-way mirror, also called two-way mirror[1] (or one-way glass, half-silvered mirror, and semi-transparent mirror), is a reciprocal mirror that appears reflective from one side and transparent from the other. The perception of one-way transmission is achieved when one side of the mirror is brightly lit and the other side is dark. This allows viewing from the darkened side but not vice versa.

  1. ^ "How to Spot a Two-Way Mirror". Snopes. Retrieved 28 March 2020.