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Devices for listening through walls

Discussion in 'Electronic Basics' started by stan, May 26, 2004.

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  1. stan

    stan Guest

    Can anyone point me to any webisite or provide me information about
    how to build a device that can listen through a concrete wall?

  2. burbeck

    burbeck Guest

    hi there stan,
    the tradishional method for a device of this type is an inverted wine
  3. burbeck

    burbeck Guest

    traditional even
  4. I'd start with a small masonry bit, sized for my microphone element...
  5. Johnboy

    Johnboy Guest

    I built one of those gadgets back in my high school days
    for science class. I glued several types of microphones
    into holes drilled in suction cups of all types. Then built
    a high gain amp and used headphones. I recall we used
    plumbers putty around the edge of the cup for use on
    locker room cinder block walls, all that was needed was an
    air tight seal. The thing worked real good and was a lot of fun.
    Not much high tech needed for this application.
  6. Speaking of walls.. I wonder what happened to the guy who wanted to use
    a dog repeller on some neighbor's mutts that were several hundred feet

    I was talking to a lady the other day and she said that they had bought
    a dog repeller to use on their neighbor's dog. They're right next door,
    and they put it on the side of their house. But she said that it had a
    very limited range, so even tho the device worked on the side of the
    house, the dog would just go into the back yard and keep on barking.
    THis unit has a bark sensing circuit, and an ultrasonic element to
    produce high levels of sound near the unit. But I guess ultrasound
    doesn't travel as far as regular sound as it gets absorbed and
    dissipates faster. So her unit isn't effective enough to cover the
    whole area. She saisd that it cost something like $70 from some company

  7. Richie086

    Richie086 Guest

    just ask im sure they will help you :)

  8. A hammer and a chisel for starters, then press your ear against the
    Seriously, if you plan to use it in a honourable way, make me believe
    that and i'd maybe help.
  9. Moto42

    Moto42 Guest

    Take a drinking glass. PLace the opening of this against the wall, and
    put your ear to the base of the glass.
  10. If you have physical access, you can put a little transmitter in the
    room ( a 'bug' .) There are various circuits on the internet you can
    use to build an FM transmitter. They are suprisingly simple to build.
    Tune it in on your stereo, and you have it.

    If you don't have physical access, then you are limited to
    amplification of some signal. The problem with this is that the
    amplification will also amplify ambient noise. You can limit this by
    attempting to muffle stray noise. Get a bucket, stuff it with rags or
    something like that, and put a microphone in the center on top. Plug
    the microphone into your stereo, put on headphones, and turn it on.
    Put the bucket against the wall, and turn it up.

    This is clearly an invasion of privacy, and possibly illegal, so I
    wouldn't actually do it.

    Bob Monsen
  11. gothika

    gothika Guest

    Well... my knowledge/experience is a bit dated.(used to work in
    surveillance year back.)
    But will share what I know.
    The do make variuos "Big Ear" microphone rigs that consist of a
    variable electret mike and amplifier with closed air headphones.
    I've seen some stick those up to a wall with some success.
    There are some mikes designed for this use as well.
    Not legal in some states I've been told. You can do a web search for
    spyshop or spystore, they'll have them for sale.
    If you can dig in the wall as suggested above you can use the method
    we used to use in the military years gone by.
    use an iron or wood spike driven into the wall with a transducer
    pickup on it fed into a amplifier rig that'll both amplify the
    vibration and shift them down to the audible spectrum.
    They also make spike mikes that do work on regular(drywall etc..)
    walls. you might predrill and give one of those a try.(you;ll have to
    judge the thickness of the cinderblock or concrete and under drill
    just a 1/16 or so to avoid detection.)
  12. gothika

    gothika Guest This link has all kinds
    of goodies for fun times. This is a good
    resource site for diy info.

    Above are a few links to places that either sell the units or plans
    for them.
    It's a start at least.
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