Two-way mirrors are most commonly used by law enforcement in questioning rooms and lineup situations, to protect the identity of the victim.
The use of two-way mirrors in public spaces is closely tied to issues of personal privacy and Constitutional rights in America. Most American states have passed additional legislation preventing the use of two-way mirrors in rest rooms, locker rooms, showers, fitting rooms and hotel rooms. If a location has chosen to use two-way mirrors as surveillance, they are required to post signs that notify you.
So instead of staring there are a few quick checks you can do to see if it is a two-way mirror.
1.Consider the Context
If you are using public facilities or somewhere you would expect privacy then it is highly illegal and unlikely to find a two-way mirror. Public conveniences usually use metal mirrors that cannot be damaged by the users.
- Look at the Installation and Lighting
Check how the mirror has been installed. Is it mounted on the wall and can you see wall behind it? If you can then there is no way it can be a two-way mirror. If it seems to be part of the wall and set into it with no gaps then there is a slight possibility that it could be a two-way mirror, but you will need to perform some further checks.
A two-way mirror is a piece of glass coated with a substance called micro pane. If you stand on the treated side, you see your reflection but the untreated side looks like a tinted window.
Note the lighting. Is the lighting incredibly bright? For a two-way mirror to be effective, the light on the mirrored side needs to be 10 times brighter than the light on the other side. If the lighting is any dimmer, it’s possible to see through the glass to the observation area.
If the mirror is hung on the wall and the lighting is dim, you are looking at an ordinary mirror. If the mirror is set into the wall and the lighting is extremely bright then read on.
- Examine the Mirror
Try to look through the glass. Bring your face right up to the mirror and cup your hands around it, blocking out as much light as possible. If the light in the observation room is brighter than the light in your room then you should be able to see into the other room.
- Shine a light on it
If you’re still not convinced, turn off the lights in your room, then hold a torch to the mirror. If it is a two-way mirror, the room on the other side should be illuminated and you will be able to see it.
- Tap on the mirror
Use your knuckle to sound it out by tapping on the mirror surface. A regular mirror will produce a dull, flat sound, since it’s placed in front of a wall. An observation mirror will produce an open, hollow and reverberating sound because there is an open space on the other side.
- The fingernail test
While not wholly accurate, if you are still looking for proof you can use your fingernail to determine if the mirror is a first or second surface mirror. Place your fingernail against the surface of the mirror. If it is a second surface mirror (normal mirror), you can’t to touch your own reflection; instead, you will see a gap caused by a second layer of glass over the mirrored surface. When you touch your finger to a first surface mirror (two-way mirror), you can touch your own reflection, since there’s no additional layer of glass in between.
However, as we said this test is not foolproof and external variables can contort the light and mirror surface.
- Smash it
This is obviously a last resort but should definitely answer the question if it is a two-way mirror or not. If it’s a two-way mirror you will break through to the observation room if it is not you will see the wall behind it. Your call!