"You can direct the beam wherever you want," Stuckey said. "It hits the sweet spot of human hearing. It's similar to having a really bright light in your eyes."
Its debilitating effect can be seen in a YouTube video of a crowd of protesters at the G20 summit in Pittsburgh in 2009. Police rolled through the street in an armored truck with an LRAD device fixed atop like a turret generating a loud sound beam into the crowd.
In an instant, the high-pitched chirping appears to compel nearly every person in the crowd to cover their ears.
In the crowd was Karen Piper, an English professor at the University of Missouri, who says she suffered immediate pain in her ears and became nauseous and dizzy. Piper said she was unable to cover her ears because she was holding bags, her purse and a camera.
"All of a sudden I heard this excruciating high-pitched noise. It was debilitating," she said this week. "I never heard anything like it before."