A two-way mirror, also known as a one-way mirror, is a mirror that is partially reflective and partially transparent. It allows people on one side of the mirror to see through it, while people on the other side see a reflection of themselves. This type of mirror is often used in interrogation rooms, police lineups, and other situations where it is necessary to observe someone without being seen.
There are several ways to tell if a mirror is a two-way mirror. One way is to look for a slight green tint in the reflection. Another way is to place your finger against the mirror. If you can see your finger behind the reflection, then the mirror is likely two-way.