It’s frightening to contemplate the possibility that any one of the mirrors you’ve looked in over the course of your life may actually have been two-way glass. It becomes even more unsettling to think that these mirrors may have been in public restrooms or changing areas.
Going forward, if you’re ever in a situation where you just aren’t sure, there are a few ways to determine whether the mirror is, in fact, just a mirror, or if it’s instead a tinted window.
Conduct A Fingernail Test
One way to check, according to wikiHow, is by conducting a simple “fingernail test.” Place your fingernail against the reflective surface in question. If there’s a gap between your nail and the mirror, it’s most likely a genuine mirror. But if you place your fingernail up to the mirror and it appears that your finger is directly touching the finger in the mirror, you might want to investigate further. Snopes points out that this test can be unreliable depending upon the size of the mirror, the angle at which it’s hanging and the lighting in the room, which is why you shouldn’t make any immediate assumptions.
Take A Peek Behind The Mirror… If You Can
Wiki-How also states that one good way to check whether or not a mirror is actually two-way glass is to see how it’s hanging on the wall. If the mirror is part of the wall, there’s a stronger chance it’s a two-way mirror. However, if you can see a wall behind it, it’s probably just a regular old mirror.
Face The Mirror
Another trick or technique Snopes recommends is to press your eyes up against the mirror and then cup your hands around your face to help block out the light of the room you’re in. If you think what you’re facing is two-way glass, you should probably be able to see somewhat of an open area behind the mirror.
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How Is The Lighting?
Observe the lighting that surrounds you. Wikihow states that 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.
Wait, Where Are You?
Answering this question alone might be able to help you determine if what you’re looking through is or is not a two-way glass. Most places that choose to use two-way glass for surveillance are required to post signs informing the public. However, if the questionable mirror is in a place where you’d expect privacy, just know that it’s illegal.
Use Your Phone’s Flashlight
By turning off the lights and holding up a flashlight to the mirror, you should be able to tell if the mirror is, in fact, two-way glass, because you’d be able to see the other side.
Give It A Tap
According to Wise Geek, two-way glass will make a different sound when tapped with your finger. This is because there likely wouldn’t be any framing or support behind two-way glass, making it sound a lot “sharper” when tapped, as you’d imagine a window would sound.
A final note: If you’re ever in doubt, alert law enforcement.
[h/t Wisdom Daily]