Two-way mirrors (or "smart glass") are legitimate tools for interrogation rooms, but they have no place in a hotel bathroom or fitting room. Here is how to tell if the glass is transparent.
Test 1: The Installation Check
Standard mirrors hang on the wall. Two-way mirrors must be set into the wall (to allow viewing from the other side). If the mirror looks recessed or part of the wall structure, be suspicious.
Test 2: The Fingernail Test
Place your finger tip against the glass.
- Gap = Safe: If there is a small gap between your finger and its reflection, it's a standard mirror (the reflective layer is on the back of the glass).
- No Gap = DANGER: If your finger touches the reflection directly ("tip-to-tip"), it is a two-way mirror (the reflective coating is on the front surface).
Test 3: The Flashlight Test
Turn off the lights in your room. Press your phone's flashlight directly against the glass. If it's a two-way mirror, the light will pass through to the observation room on the other side, illuminating unauthorized equipment or people.