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Have you stood in front of a mirror and wondered if someone is spying on you?

In this article, we’ll show you several easy techniques for detecting a two way mirror.

A two way mirror is a transparent mirror that can look exactly like a regular mirror when the back side of it is dark. Don’t worry, there is more than one way to tell the difference!

Techniques

Test #1

Fingernail Test

Test #2

Tint Comparison

Test #3

Hollow Sound

We have a series of three tests to use to confirm that the mirror you see in front of you is not a two way mirror.

Test #1: The Fingernail Test

What is the fingernail test?

Place your fingernail to the front of the mirror. You can test to see which side the reflective coating is facing. For glass two way mirrors, the mirror coating has to be facing you.
 
If your fingernail’s reflection touches itself, that is the coated side. If there is a gap between your finger and its reflection, go to Test #2.

The Fingernail Test Rules Out the Glass Two Way Mirror

The glass two way mirror is one-directional. You can only install it with the mirror coating facing forward so it is easy to spot using this test.
 
The acrylic two way mirror and glass smart mirror are not one-directional. You must use the next two tests to be sure it is not a two way mirror in this case.
fingernail-test-with-acrylic-and-glass-two-way-mirrors

More on the Glass Two Way Mirror

The glass two way mirror has a mirror coating that is 70% reflective. It only allows 11% of the light through the mirror. It is on a dark grey substrate, which makes it one-directional. The glass two-way mirror cannot cheat the fingernail test. The reflection coating must be facing the room that is being observed. That way the people being observed are only seeing their reflection. On the opposite side, the darker room is located where the observer will be watching.

Notice the fingertip’s reflection touching itself. Very different from that of the standard mirror’s reflection.

The light is even on both sides of the mirror in this picture. You are able to see through the semi-transparent glass at the moment.

Front

Side

Back

Glass two-way mirror cannot cheat the fingernail test. The reflection coating must be facing the room that is being observed. That way the people being observed are only seeing their reflection. On the opposite side, the darker room is located where the observer will be watching.

Test #2: Tint Comparison

How does a two way compare to a standard mirror?

All three mirror types we are looking at in this article have a 70% reflection. A standard mirror is 94% reflective. This means that it will have a darker tint than a standard mirror.

Bring a Small Makeup Mirror With You

To do this test, simply pull out a standard mirror from your purse or pocket. Put it up next to the mirror and check to see if the tint looks the same as your mirror. If it appears darker, it is likely a two way mirror.

More on the Acrylic Two Way Mirror

70% reflective with 25% light transmission on a grey substrate, acrylic two way mirror is reflective from both sides of the substrate. Meaning it can be installed either way. If installed backwards ( the coated side on the back ) it can cheat the fingernail test looking like the reflection of a standard mirror! Something to think about if you are testing a questionable mirror. Acrylic tends to have a different feel than glass. Rubbing your nail gently across the surface may help you determine if you have found an acrylic two way mirror, or a standard glass mirror.

Acrylic two way mirror will closer match the reflection tint of a standard mirror as well. Whereas glass two way mirror tends to have a bronze tint.

More on the Glass Smart Mirror

Smart mirror is similar to the acrylic two way mirror in properties. It has a 70% reflection with a 25% light transmission. Its reflective from both sides of the substrate. Smart mirror can be installed backwards as well ( the coated side on the back ) it can cheat the fingernail test looking like the reflection of a standard mirror!

If you are testing a questionable mirror, smart mirror tends to have a warmer tone on the reflective coating. Observe the smart mirror on the right compared to the standard mirror reflection of the mug on the left.

Test #3: Knock on the Mirror

Listen for a Hollow Sound

If you are worried about a two way mirror and the first two tests did not work for you, try knocking on the mirror gently. If there is a hollow sound going on instead of a more solid sound, it is possible that the area behind the mirror is open instead of the mirror being just mounted to the wall. This could reveal that there is an observation area or a camera behind the mirror. Be careful out there!

Did you know?

Two-way mirrors are dependent upon the lighting in the room. Both sides of the mirror cannot be evenly lit for the illusion to work. The observer side of the mirror must be at least half as dark for the reflection coating on the other side to properly reflect light back at those being observed.

Want to see samples of two way mirrors?

Visit our ORDER SAMPLES page.

CONCLUSION: Now that you are armed with knowledge, never be afraid of a sketchy looking mirrors again. Just remember the fingernail test & a makeup mirror.

This Post Has 21 Comments

  1. As there are lots of ways to detect the two ways mirror as this mirror can be detected easily by touching the nails and by fingerprints easily without any hassle you can detect the two-way mirror. As there are too many ways to which can be easily detect the two-way mirror but these are the correct and easy way to detect the mirror.

  2. Hi, you have an extraordinary artfulness recorded as a hard copy the websites. Continue composing more on these lines. Appreciated perusing this, extraordinary bits of knowledge. Much obliged!

    1. Both and how much of each is going to be dependant mainly upon it’s reflective properties or the properties of the reflective coating. For instance let’s say the mirror’s reflective coating is rated at 74%. Very simply the laser , just as any light is only going to be able to emit 21% of it’s light while 74% is going to be reflective back into your side of the mirror. While I may have slightly over simplified my answer, there are a few other factors to consider. The color of the laser along with the color of the reflective coating is just one of these other factors to consider when calculating the amount of laser light that will, both, be reflected and just how much of your beam passes through. How powerful your laser is and the amount of time you allow your Lazer to stay focused on a particular spot on your mirror may also affect the amount of light that gets through…eventually that is. Because laser beams tend to be hot; if a beam is allowed to stay focused on a particular spot on your mirror the reflective coating material will eventual become vaporized and allow even more of its light to pass through.

  3. Both and how much of each is going to be dependant mainly upon it’s reflective properties or the properties of the reflective coating of the mirror. For instance let’s say the mirror’s reflective coating is rated at 74%. Very simply the laser , just as with any other type of light is only going to be able to emit 21% of it’s light pas⁶6t the coating while 74% is going to be reflective back into your side of the mirror. While I may have slightly over simplified my answer, there are a few other factors to consider. The color of the laser along with the color of the reflective coating is just one of these other factors to consider when calculating the amount of laser light that will, both, be reflected and just how much of your beam passes through. If your lasers light beam color is red (lame) and the mirror’s coating has a red tint to it then your beam maty be reduce in the amount of light is allowed to pass-through in the red spectrum due to the filtering affect. Because the red tint will tend to absorb some or all of the red light trying to pass through thus decreasing, both, the reflective and pass through amounts of light
    How powerful your laser is and the amount of time you allow your Lazer to stay focused on a particular spot on your mirror may also affect the amount of light that gets through…eventually after some amount of time that is. Because laser beams tend to be hot; and if a hot
    beam is allowed to stay focused on a particular spot on your mirror the reflective coating material will eventually begin to degrade an become vaporized and allow even more of its light to pass through. While I did say that this could eventually happen over time there are many high powered lasers that could punch through this coating in an instance and some are impressive enough that thy could vaporize the glass mirror itself allowing 100% to pass-through regardless of your reflective coatings.

  4. Both, how much of each is going to be dependant mainly upon it’s reflective properties or the properties of the reflective coating of the mirror. For instance let’s say the mirror’s reflective coating is rated at 74%. Very simply the laser , just as with any other type of light is only going to be able to emit 21% of it’s light pas⁶6t the coating while 74% is going to be reflective back into your side of the mirror. While I may have slightly over simplified my answer, there are a few other factors to consider. The color of the laser along with the color of the reflective coating is just one of these other factors to consider when calculating the amount of laser light that will, both, be reflected and just how much of your beam passes through. If your lasers light beam color is red (lame) and the mirror’s coating has a red tint to it then your beam maty be reduce in the amount of light is allowed to pass-through in the red spectrum due to the filtering affect. Because the red tint will tend to absorb some or all of the red light trying to pass through thus decreasing, both, the reflective and pass through amounts of light
    How powerful your laser is and the amount of time you allow your Lazer to stay focused on a particular spot on your mirror may also affect the amount of light that gets through…eventually after some amount of time that is. Because laser beams tend to be hot; and if a hot
    beam is allowed to stay focused on a particular spot on your mirror the reflective coating material will eventually begin to degrade an become vaporized and allow even more of its light to pass through. While I did say that this could eventually happen over time there are many high powered lasers that could punch through this coating in an instance and some are impressive enough that thy could vaporize the glass mirror itself allowing 100% to pass-through regardless of your reflective coatings.

  5. Thank you for this! It’s super helpful AND timely, I will be using this tips for my own clients so that there MH Fine Hardware go smoothly. And thanks in advance for your time. I’m so excited I found your blog through this — it’s all so beautiful and the topics so well-organized/helpful!

  6. I think I’ll just cover all the mirrors in hotel rooms. No reason to put myself in a possible bad situation. Now I worry if the mirrors can swing open and someone come in while I sleep. Ok I may have watched too many movies! lol 😂

  7. Hardness (scale):
    Glass 5.5-7
    Acrylic 2.5-3.5
    As glass is significantly harder, it’s more resistant to scratching. Use a coin or keys to scratch the mirror – these shouldn’t scratch glass, but will scratch the plastic. You can also use a needle/nail, a rock, or the uneven surface on the bottom of a porcelain plate.

  8. Hello,

    I have a touch screen and ı wanna cover a mirror photobooth please contact me for details

  9. Of the methods I know, shed light on them. If you are not convinced yet and have doubts, turn off the lights in the place, then turn on a flashlight and point it at the mirror (you can even use your mobile phone’s “flashlight”). The opposite side should be visible and you can see it.

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