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Thread: Making a nice box into a faraday cage

  1. #1
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    Making a nice box into a faraday cage

    I have a relative who is a cyber security expert. He is an “ethical hacker” for a major corporation. He leads a team that tries to break in to corporate data in order to strengthen their security. Recently I queried him about an incident where I discussed a health issue with my doctor and moments later was served up ads for dealing with that issue. My relative walked me through a few settings and told me that my phone was the likely culprit. Even though it was locked and in my pocket, the phone was listening for potential advertising. My relative told me that when he wants to have a truly private conversation with his fiancée, they put their phones in the microwave.

    It occurs to me that it might be nice to make them a nice little box that would block RF and attenuate sound. So can I just buy some faraday cloth from Amazon and line the box? Are there any special tricks?

  2. #2
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    Faraday cloth? Just line it with metal foil then glue felt over it. need some sort of metal J weatherstrip on the opening. Metal hinges would complete the circuit. I do not think they need any grounding
    Bill D

  3. #3
    If I remember my classes in electrical engineering, a Faraday cage can have holes in it as long as the holes are smaller than the wavelength of the RF. I think most people would aim for holes no bigger than a quarter wavelength.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

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    do not forget the bottom.
    Bill D

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    I looked it up wifi or bluetooth will be about 6cm. Cellphone a little longer so I would say about 1cm hole or smaller. Solid sheet is fine as well. metal window screen is probably the cheapest and easiest to find. You could make it like a birdcage.
    No idea what a charging mat and cord to the inside would do to the faraday effect.
    A metal cookie box would be ideal. Use a bonding strap to connect top and bottom. Metal box with wood box inside, lined with felt. Then wood either glued or made as a separate piece on the outside. look at humidors for style ideas. A antique kitchen dough box comes to mind or a snapon tool chest.
    Bill D
    Last edited by Bill Dufour; 05-14-2021 at 12:41 AM.

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    What phone do you use?

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    Does your phone have a shutoff button?

    https://www.irda.org/rfid-key-fob-protector

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    Many years ago I spent a year in the shadow of a large military radar installation. Hi-fi equipment (remember that? This was when it had tubes and wiring.) would buzz badly. We made wooden cages with copper window screen for shielding and grounded it. That worked well.

    But is it possible the cyber security expert was pulling your leg? If you shield the phone's signal you block it from the cell tower. Having a conversation from inside the microwave sounds like fodder for a comedy show. If it really does work then you have an easy solution: buy an old microwave. But I don't think that will help with a situation like you described with the phone in your pocket.

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    Putting them in a faraday cage will most likely mean you will not get texts or phone calls. However if you are worried about your phone hearing you speak a faraday cage will do nothing to stop it as it only blocks electrical signals, not sound waves.

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    Thanks Bill,
    does the mesh have to be earth grounded?
    if I have a box with a hinged lid, does the mesh in the lid have to connect with the mesh in the box?

  11. #11
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    Quote Originally Posted by Alex Zeller View Post
    Putting them in a faraday cage will most likely mean you will not get texts or phone calls. However if you are worried about your phone hearing you speak a faraday cage will do nothing to stop it as it only blocks electrical signals, not sound waves.
    my plan would be to muffle the sound as well as the RF.

  12. #12
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    To see a faraday cage you can sit in and get hit by ten foot lightning bolts check out Spark Museum.org
    Steve Jenkins, McKinney, TX. 469 742-9694
    Always use the word "impossible" with extreme caution

  13. #13
    Quote Originally Posted by Alan Rutherford View Post
    But is it possible the cyber security expert was pulling your leg?
    I wonder this, also. If your phone is listening to everything you say, some very technical people would have discovered it by now and published a report on it. I think if it was shown to be the case, there would be a very strong reaction against the company. I kind of doubt if a company would be willing to get into that position.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  14. #14
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    Quote Originally Posted by Roger Feeley View Post
    My relative told me that when he wants to have a truly private conversation with his fiancée, they put their phones in the microwave.
    Don't think I'd do that. Didn't our past Supreme administration tell us how our microwaves were spying on us.
    Confidence: The feeling you experience before you fully understand the situation

  15. #15
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    Any phone that has a voice activated assistant has to listen to you all the time. What it actually does with that is another issue but I am not surprised there is advertising based off what it listens to. Probably part of some EULA that nobody reads.

    From what I have been told by computer tech people (from the law enforcement side) a microwave doesn't work as a faraday box. It helps but isn't perfect. Airplace mod keeps anything from coming in but won't stop the apps from hearing.

    The best answer is above. The off button. Anything a faraday cage does for you the off button will also do. LE used a faraday box to keep people from remotely wiping the phone, since you don't need that just turning it off is as good. Turning it back on is the same as taking it out of the cage. The downsides to turning phones off is in being able to access them against the wishes of the owners nothing that will effect a personally owned phone.

    Joe
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    For best results, try not to do anything stupid.

    "So this is how liberty dies...with thunderous applause." - Padmé Amidala "Star Wars III: The Revenge of the Sith"

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