First off, some people call them “two-way mirrors” and some call them “one-way mirrors.” Whatever. You know what I am referring to. It’s that type of glass that is a mirror on one side and a window on the other.

A number of motels have mirrors on the wall. Orchard in Pasig has mirrors in almost all the walls. If you have viewed my massage parlor videos at Vimeo, you may have noticed that some massage parlor rooms have mirrors as well.

Are these mirrors “two-way mirrors?” How does one detect “two-way mirrors?”

A quick Google pointed me to several articles. How Stuff Works and Wiki How have given logical and common-sense approaches.

A two-way mirror relies on the lighting. The room with the reflective surface has to be kept very brightly lit, so that there is lots of light to reflect back from the mirror’s surface. The other room, the one used by the voyeur, must be kept dark, so there is very little light to transmit through the glass. That is one reason why, when one peers through the showroom aquarium, the room with the attendants is harshly lit and the room with the guests is subtly lit. So if you want to check if there are some Hayden-wannabe perverts peering behind that mirror, turn off the lights in your room and then shine a flashlight through the “mirror.” If it is a two-way mirror, you should be able to see the chamber behind it.

Another way is to press your eyes against the mirror and cup them with your hands, creating a dark “tunnel” to block out the light. We all do this when we want to peer through a car with a dark, highly-reflective tint. Same principle.

Finally, an ordinary mirror is set against a solid wall while a two-way mirror is not. Tapping on an ordinary mirror will produce a dull sound. A two-way mirror is fundamentally a window so tapping on it will produce a hollow sound.

A reader of my site commented that owners of motels and massage parlors are unlikely to allow two-way mirrors because “privacy/secrecy is the core attraction for these enterprises” and “the moment this gets tainted, that’s it for their entire business.” Even word-of-mouth can damage their business. What advantage is there in putting up a two-way mirror? Politicians and celebrities don’t go to motels. The risk (loss of revenue from guests) is not worth the reward (a scandal video which gives no monetary benefit). Besides, scout around the internet—have you seen a video shot through a two-way mirror in a motel?