Pizeo Buzzer as a **Microphone Bug**

Discussion in 'Wireless & RF Design' started by EricaStone, Apr 1, 2015.

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  1. EricaStone

    Thread Starter New Member

    Apr 1, 2015
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    Hello there

    My work telephone uses a piezoelectric buzzer to create the ringtone for a call alert.

    I suspect that the buzzer is being used to record room audio. I also suspect the recorded audio is then transmitted via RF. I'm not referring to a phone tap. Taps record telephone call conversations. This is a bug which records every sound that occurs in the room.

    Ive disassembled many phones at our company and noticed that certain individuals have the polarity on the pizeobuzzer reversed. The phones that I suspect are compromised have the positive lead (red wire) connected to the positive terminal while the untampered phones have the negative lead (black wire) connected to the positive terminal.

    By reversing the polarity is it possible to record room audio? Or would it allow for a carrier frequency to interact with the buzzer such that modulated RF would be emitted?

    Here are some pictures of the telephone circuitry and buzzer:
    http://bit.ly/1I0AYsd
    http://bit.ly/1FdMcpB
    http://bit.ly/1C1PoQh

    Any help would be appreciated as I'm not an electronic/avr engineer.
     
  2. DickCappels

    Moderator

    Aug 21, 2008
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    Reversing the wires to passive piezoelectric transducers does not have any effect on their operation as far as I know, and I have used a lot of them.
     
  3. EricaStone

    Thread Starter New Member

    Apr 1, 2015
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    Incidently I just stumbled upon this

    "Reversing the polarity of the D.C. voltage cause the ceramic plate to shrink, bending the metal plate in the opposite direction, shown in Figure 101(b)"

    From: Piezoelectric Sound Components

    I'm going to do a couple of tests on this buzzer by reversing the polarity.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    If a spy wanted to bug your telephone they would not need to use the buzzer as a microphone.
     
  5. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    I have my doubts...

    I agree

    As a matter of fact, beside "reversing" the buzzer, there would have to be supporting circuitry to listen and transmit the audio. It is unlikely IMHO that all phones have this circuitry as a default.
     
  6. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Why employees are taking apart their company's telephones is a bit of a mystery.
     
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  7. alfacliff

    Well-Known Member

    Dec 13, 2013
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    when used as a sound generator or microphone the only thing polarity does is to set the direction it flexes, not whether it is a microphone or not. if it had voltage across it, it would not make a very good microphone. the phones with piezo speakers use a circuit inside to generate the ring tone, it is not across the phone lines.
     
  8. EricaStone

    Thread Starter New Member

    Apr 1, 2015
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    I tested the buzzer. Its a great microphone. And you're right with a voltage across its not a microphone any more.
     
  9. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Have you checked the wall outlets, ceiling panels and under your desk for hidden microphones? Is this an April fools joke?

    Erica also posted the same query on the AVR forums, and also managed to spend $2,600 on a bug detector.

    How do we know it's not you trying to find a way to bug the phones in your office?

    PS Your employer can easily monitor your email and web habits on company computers. Hope you're not posting this at work.
    Boss here. Stop taking the companies phones apart.
     
    Last edited: Apr 1, 2015
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  10. EricaStone

    Thread Starter New Member

    Apr 1, 2015
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    I've got a stalker
    I always wanted one
     
  11. EricaStone

    Thread Starter New Member

    Apr 1, 2015
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    This is not an April's fool joke
     
  12. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    As far as I can tell, there is nothing on that PCB suggesting an ability to transmit RF effectively.

    Reversing a piezo element does not turn it into a microphone...it is a microphone already, albeit a really bad one.

    I think you are being paranoid. But, then again, maybe the whole world really is out to get you...
     
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  13. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Why would you assume your stalker bugged your work phone?

    Tell your employer and seek legal council. It would have cost you less to hire a P.I. than assume your stalker is tech savvy enough to take your phone(s) apart and install bugs. Almost all companies have harassment rules.

    Bad news, audio eavesdropping bugs can be almost anything. They can simply store recordings till retrieved so your RF detectors will do nothing. Watches, Pens, Light bulbs... Don't do this yourself, get real legal council (not forum advice).
    [​IMG]
     
  14. EricaStone

    Thread Starter New Member

    Apr 1, 2015
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    Thank you for taking the time to analyse the ciruitary.

    I've seen a YouTube video that said that buzzer will only output audio if the positive terminal is connected to the positive wire. That's how the bugged phones are arranged. The unbugged phones have the black wire attached to the positive terminal.

    I just connected the buzzer to an amplifier and its an excellent microphone!
     
  15. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Why are you convinced it's your phone that's bugged? Why haven't you talked to your employer or gotten legal advice?

    How about a laser listening device? Any glass surface should work.
    http://en.wikipedia.org/wiki/Laser_microphone
     
  16. EricaStone

    Thread Starter New Member

    Apr 1, 2015
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    Hello there

    I'm back again

    As a refresher:
    Hello there

    I'm convinced my landline telephone at work is bugged.
    Its being used to transmit all room conversations when the phone is on-hook.

    After inspecting about seventy telephones I found that those phones which I suspect to be bugged at work all have the polarity around the ringer correctly fixed. The bugged phones have positive lead (red wire) connected to the positive terminal and negative lead (black wire) connected to the negative terminal. The clean phones have this connection reversed i.e. positive lead to negative terminal and negative lead to positive terminal. The ringer is a piezoelectric transducer.

    Here are pics of the circuit:
    http://bit.ly/1C1PoQh
    http://bit.ly/1I0AYsd
    Note the ringer is the black object seen in the pics.

    I just recently came across an article describing how piezoelectric transducers can be used to transmit and eavesdrop:
    http://www.reddit.com/r/badBIOS/comments/2e3yuv/badbios_transmits_ultrasound_via_piezo_can/

    Can the ringer circuit on this telephone together with the piezoelectric ringer be used to transmit room audio via RF?
    P.S. I verified that the ringer can act as a microphone by connecting it to an amplifier.
     
  17. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    What makes you suspect those particular phones are bugged?
     
  18. DickCappels

    Moderator

    Aug 21, 2008
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    The answer to your question is "no".

    Would you please tell us the make and model of the telephones? Also, if you have the schematic of the phone or PCB that might help as well.
     
  19. EricaStone

    Thread Starter New Member

    Apr 1, 2015
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    Well this is a long story, a few employees are ex-military in our department. I suspect they are behind this and they are part of a bigger circle in our organisation.
    I've already been threatened by them because they suspect I know something. I just can't prove that audio is transmitted by the phone.

    This phone is also used in department stores, every phone that I inspected at the department store has the black lead to the positive terminal.
    The phones of the employees who are ex-military have black lead to positive terminal. So are the phones in the elevators, conference rooms, canteens etc.
    My office phone and that of my friends and some colleagues are the only phones that have positive lead to positive terminal and negative lead to negative terminal.

    In the "bad bios" article they mention something about "grounding" could this contribute to an antenna functionality?
    I'm not an electronic engineer so I have no clue what this all means.
     
  20. OBW0549

    Well-Known Member

    Mar 2, 2015
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    No.

    Don't feel bad; the nut-job who wrote that article clearly was not an engineer, either, and had no more clue what he was talking about than you do. That article is some SERIOUSLY paranoid sh*t, as well as being chock-full of "voodoo electronics theory."
     
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