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And what kind of device I need to use for eavesdropping?

Actually a microphone with a parabolic reflector or laser reflected listening devices available on the market but is there any other devices on the planet which should allow to eavesdrop at least 2-3kilometers?

Which tools and what kind of knowledge I need to know for manufacturing an ultra long distance/range eavesdropping device?

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closed as off-topic by John Rennie, heather, ACuriousMind, John Duffield, dmckee Aug 27 '16 at 17:16

  • This question does not appear to be about physics within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 4
    $\begingroup$ I'm voting to close this question as off-topic because it isn't a question about physics $\endgroup$ – John Rennie Aug 27 '16 at 10:30
  • $\begingroup$ @JohnRennie I think it is about physics, but matches better engineering. $\endgroup$ – peterh Aug 27 '16 at 14:46
  • $\begingroup$ Nah, it's not about physics, in the sense encapsulated by our engineering close reason. $\endgroup$ – David Z Aug 27 '16 at 18:23
  • $\begingroup$ This is a motivated question and I see no reason to close it. Physical conditions sets the limit for such a device. Sound can however be detected from very much longer distance than the sound can travel with use of laser vibrometers: en.wikipedia.org/wiki/Laser_Doppler_vibrometer $\endgroup$ – David Jonsson May 4 at 19:43

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