How to Identify a Two-Way Mirror

Two-way mirrors are commonly used in police stations and various types of interrogation rooms to give unseen observers an anonymous view. However, this special glass is not difficult to find and purchase. If you have a suspicion that you’re being spied upon through a two-way mirror, there’s an easy way to be sure.

Instructions

Difficulty: Easy

Things You’ll Need:

• Possible two-way mirror
• Flashlight

1. Press your fingernail right up against the glass and look closely. If you see a gap between your fingernail and its reflection, the mirror is not two-way. If your fingernail touches its reflection, it is possible that the mirror is two-way.
2. Knock on the mirror. If the sound is hollow, your case for a two-way mirror is even stronger.
3. Turn off the lights in the room and shine a flashlight into the mirror. If it is a two-way mirror, you should be able to see the light shining beyond the mirror surface and into the next room.

Tips & Warnings

• It is possible that all of these tests, with the exception of the fingernail test, can fail to help you identify an actual two-way mirror. If there is simply a small, hidden camera on the other side of two-way glass as opposed to an entire observation room, the knock and light tests are unlikely to provide any usable evidence.