The U.S. military bankrolled early development of a non-lethal microwave weapon that creates sound inside your head, instead of using high power to create an intolerable noise, it might be used at low power to produce a whisper that was too quiet to perceive consciously but might be able to subconsciously influence someone. The directional beam could be used for targeted messages, such as in-store promotions. Subliminal advertising, beaming information that is not consciously heard . While the effectiveness of subliminal persuasion is dubious, I can see there might be some organizations interested in this capability. And if that doesn't work, you could always point the thing at birds. They seem to be highly sensitive to microwave audio, so it might be used to scare flocks away from wind farms -- or shoo pigeons from city streets.
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