[Bouncer]

True; it would be a form of psychological camouflage. There are speaker systems available to the public which can do this! The technology is based on ultrasonic heterodyning, meaning that if they aimed it at you, it would sound like it was coming from your own head. What's more, you can bounce the UH signal off solid objects, so the "voice" would appear to emanate from a bulding, automobile, or possibly another person, and YOU would be the only one who hears it.

http://ghostphysics.blogspot.com/2005/01/evp-background-information.html

Any jerk with the money and a little know-how could be terrorizing whole families, and the cops are clueless.