Detecting Two-Way Mirrors

Would-be peeping toms still resort to less technologically advanced methods such as peepholes and two-way mirrors. So if you are spooked by the likelihood that innocent-looking mirrors in hotels and motels are two-way mirrors, the other side of which could have a camera spying on you, here are some precautions excerpted from Snopes.com: Two-way mirrors, or transparent mirrors, are laminated coated glass products that have been treated with Mirropane on the first surface of the glass. They're also known as "observation mirrors" and are commonly used in settings (such as police stations, schools, and businesses) where there is a need to conduct unobtrusive monitoring for safety and security purposes.

Transparent mirrors are most obviously distinguishable from ordinary mirrors in that they're not hung on walls as ordinary mirrors are. They're set into walls (or doors) as windows are. In other words, if there's a wall behind a mirror, the mirror is almost certainly an ordinary one — a transparent mirror would be part of the wall itself. Also, the lighting in front of a transparent mirror must be much brighter than the lighting on the other side (where the hidden observers are) for it to work effectively, and some light leaks through from the brighter side to the dimmer side. According to the folks in Mirropane's technical support group, you can use these factors to your advantage by pressing your eyes up against the mirror and cupping your hands around them (to block out the light from the room you're in): if you're truly dealing with a transparent mirror, you should be able to see at least a little something of the open area behind it. Also, rapping on the mirror should provide an aural clue: ordinary mirrors have backings and are usually placed against walls, so rapping on them will generally produce dull thuds; transparent mirrors are set into walls with open areas behind them, so rapping on them should produce much more open, hollow sounds. Debunking the email hoax that suggested doing a fingernail test a few years ago, TwowayMirrors.net also says that the best way to detect a two-way mirror is with a laser pointer or good flashlight. If you hold the flashlight or laser pointer against the surface of the mirror, you will be able to see the beam of light go through.