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There's this message spreading virally over the internet:

Read This Message.....!!!!

How to Detect Hidden Camera in Trial Room?

In front of the trial room take your mobile and make sure that mobile can make calls........ Then enter into the trail room, take your mobile and make a call..... If u can't make a call......!!!! There is a hidden camera...... This is due to the interference of fiber optic cable during the signal transfer......

Please forward this to your friends to educate this issue to the public......To prevent our innocent ladies from HIDDEN CAMERA...........

Pinhole Cameras in Changing Rooms of Big Bazaar, Shoppers Stop?

A few days ago, I received this text message: Please don't use Trial room of BIG BAZAAR there are pinhole cameras to make MMS of young girls. So, please forward to all girls. Also forward to all boys who have sisters and girlfriends.

Don't be shy in forwarding this message. Because its about protecting the integrity of all girls & ladies.

HOW TO DETECT A 2-WAY MIRROR?

When we visit toilets, bathrooms, hotel rooms, changing rooms, etc., How many of you know for sure that the seemingly ordinary mirror hanging on the wall is a real mirror, or actually a 2-way mirror I.e., they can see you, but you can't see them. There have been many cases of people installing 2-way mirrors in female changing rooms or bathroom or bedrooms.

It is very difficult to positively identify the surface by just looking at it. So, how do we determine with any amount of certainty what type of Mirror we are looking at?

CONDUCT THIS SIMPLE TEST:

Place the tip of your fingernail against the reflective surface and if there is a GAP between your fingernail and the image of the nail, then it is a GENUINE mirror.

However, if your fingernail DIRECTLY TOUCHES the image of your nail, then BEWARE, IT IS A 2-WAY MIRROR! (There may be someone seeing you from the other side). So remember, every time you see a mirror, do the "fingernail test." It doesn't cost you anything. It is simple to do.

This is a really good thing to do. The reason there is a gap on a real mirror, is because the silver is on the back of the mirror UNDER the glass.

Whereas with a two-way mirror, the silver is on the surface. Keep it in mind! Make sure and check every time you enter in hotel rooms.

Share this with your sisters, wife, daughters, friends, colleagues, etc.

Pass this message to all Ur friends in the Contacts.

Examples of web-sites that have picked up and publish the claims include:

The essence of the message is that, you can detect a hidden camera in trial rooms simply by attempting to make a call from inside the room. If the call fails, there probably is the camera in the room. They say this happens because of "interference of fiber optic cable during signal transfer". I am unable to understand this phenomenon. Does this test actually work? If yes, how?

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20  
No, the hidden camera probably isn't using fibre optic cable. No, the phone isn't affected by fibre optic cable. No, cameras don't necessarily affect phones in other ways. (Evidence: use your phone, while someone else takes a picture with their smartphone - it is a wireless camera.) None of this is proof, hence not an answer. –  Oddthinking Sep 1 '11 at 6:47
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Oh, and the mirror claim is bunk too - They are often aluminium, not silver; there's no reason a sheet of glass couldn't be between the mirrored surface and the bright room. Every one that I have seen could be detected by walking up very close to mirror and shading your eyes, so it was darker on my side that the room beyond. –  Oddthinking Sep 1 '11 at 6:51
4  
Chain / hoax mail claims do not seem notable enough to seriously check. –  Suma Sep 1 '11 at 8:20
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How to detect a BS-Email: It starts with an advice to do, what you're already doing, like Read This Message. It doesn't know what it wants to say, and uses multiple dots therefore: ...... It thinks, you're a moron, and need 4 exclamation marks, to understand what you wouldn't understand with a single one!!!! –  user unknown Sep 1 '11 at 10:15
5  
@Oddthinking: With "trial room" the first thought that came to mind for me was a criminal trial being conducted in a court room. –  Randolf Richardson Sep 1 '11 at 16:04

2 Answers 2

up vote 36 down vote accepted
  1. This is due to the interference of fiber optic cable during the signal transfer - False. Fibre optic cables do not interfere with other electronics, and the camera almost certainly isn't using one anyway. Any interference from the camera/cables is likely to be comparable to the amount provided by the webcam in your laptop, and the various cables at your desk, so they would not affect your mobile signal.
    While a lack of signal may be evidence of a mobile signal jammer, it may also be the thick walls of the room. That's all you can say.

  2. Place the tip of your fingernail against the reflective surface and if there is a GAP between your fingernail and the image of the nail, then it is a GENUINE mirror. - This is false. A one-way mirror is a piece of glass that is dark on one side, and brightly lit on the other, with a coating of aluminium on one, or both sides. This means it could be coated behind the pane of glass, and this test would not work. Also another piece of glass can be placed in front anyway.
    As for the reverse - cheap mirrors can be made with rolls of mirror-like material, that does not have glass in front of it. This material will fail this test, but cannot be used as a two-way mirror.

Sources: Common sense. If you want something more concrete, you can learn about Electromagnetic interference and optics in any GCSE or equivalent physics text book.

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This post does not cite any references or sources. Please help improve this post by adding citations to reliable sources. Unsourced material may be challenged and removed.

5  
Obviously, I agree with you, but without any empirical evidence to support it, this is still just speculation. Please provide some references to support your claims. –  Oddthinking Sep 1 '11 at 14:10
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1. For the note about the fibre optic, this seems to be a logical statement to me because it is a well-known fact that light doesn't cause interference with electronics or radio-waves like electricity can. 2. Regarding detecting if a mirror is "genuine," I agree that it would be beneficial to see evidence supporting that information. –  Randolf Richardson Sep 1 '11 at 16:02
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The fiber optic part falls in the "so obvious it doesn't need a reference" category. –  DJClayworth Sep 1 '11 at 16:35
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@DJClayworth, I am torn. If it is that obvious, then does the claim need our attention at all? –  Oddthinking Sep 1 '11 at 17:00
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I wouldn't want to downvote a question because it could be refuted with high school science. Lots of people don't know high school science. –  DJClayworth Sep 1 '11 at 20:24

The trick for detecting a 2-way mirror is not 100% reliable, but is not entirely wrong either. Two-way mirrors intended for observation are made using dark ("smoked") glass (/acrylic/whatever), with a partially-reflective coating on one side. Critically, the reflective side is installed toward the subject (i.e. the one being spied on).

The reason for this is that the dark glass makes the observer's side appear even darker than it really is -- Pilkington's Mirropane Guidelines gives a recommended scenario where the subject's reflection is 50 times brighter than their view of the observer, and the observer's relection is 5.5 times dimmer than their view of the subject; this is a result of a combination of the lighting on the two sides (8x brighter on the subject side), reflectivity of the coating, and attenuation through the acrylic (compare R_f and R_g in the PDF). It also says:

Where an 8 to 1 light ratio cannot be achieved, an additional light [layer? -GD] of grey glass can be added, to the glass side of the transparent mirror, by either multiple glazing or lamination, to obtain a satisfactory Masking Ratio. This will however, reduce the brightness of the observer’s image of the subject.

Note that it's possible that someone could put another layer of glass in front of the reflective side, or use a partially-reflective mirror with normal glass (though I don't know if anyone makes this in large sizes -- it's normally small pieces used for optics work) and an even higher light ratio. But those don't seem terribly likely...

Normal mirrors, on the other hand, are generally second-surface mirrors -- that is, the reflective layer is behind the glass. There are exceptions, for example I've seen mirrors in freeway rest stops with no glass at all, just polished metal. But they're the exception, not the rule.

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