One-way mirror

Glass that allows people on one side to see those on the other but not vice versa

A one-way mirror, also called two-way mirror (or one-way glass, half-silvered mirror, and semi-transparent mirror), is a mirror that appears reflective from one side and transparent from the other. The perception of one-way transmission is easily achievable 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.

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