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?


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

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    $\begingroup$ 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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