PITTSBURGH — Police ordered protesters to disperse at the Group of 20 summit last week with a device that can beam earsplitting alarm tones and verbal instructions that the manufacturer likens to a "spotlight of sound," but that legal groups called potentially dangerous.

In this Thursday Sept. 24, 2009, file photo an unidentified person holds his ears to avoid sound coming from the Long-Range Acoustic Device approaching from left during clashes between protesters and Pittsburgh police in Pittsburgh during the G-20 Summit . Police dispersed protesters at the Group of 20 summit last week with a Long-Range Acoustic Device that emits a beam of earsplitting alarm tones that the manufacturer likens to a "spotlight of sound," but that legal groups called potentially dangerous. (AP Photo/Philip Scott Andrews, File) The device, called a Long Range Acoustic Device, concentrates voice commands and a car alarm-like sound in a 30- or 60-degree cone that can be heard nearly two miles away. It is about two feet square and mounted on a swivel such that one person can point it where it's needed. The volume measures 140-150 decibels three feet away — louder than a jet engine — but dissipates with distance.

Robert Putnam, spokesman for the manufacturer, San Diego-based American Technology Corp., said it's "like a big spotlight of sound that you can shine on people."

"It's not a sonic cannon. It's not the death ray or anything like that," Putnam said. "It's about long-range communications being heard intelligibly."

During the Pittsburgh protests, police used the device to order demonstrators to disperse and to play a high-pitched "deterrent tone" designed to drive people away. It was the first time the device was used in a riot-control situation on U.S. soil, according to American Technology and police.

Those who heard it said authorities' voice commands were clear and sounded as if they were coming from everywhere all at once. They described the "deterrent tone" as unbearable.

Joel Kupferman, who was at Thursday's march as a legal observer for the National Lawyer's Guild, said he was overwhelmed by the tone and called it "overkill."

"When people were moving and they still continued to use it, it was an excessive use of weaponry," Kupferman said.

Witold "Vic" Walczak, legal director for the American Civil Liberties Union in Pennsylvania, said the device is a military weapon capable of producing permanent hearing loss, something he called "an invitation to an excessive-force lawsuit."

The operator of the device is usually behind it and not in the path of the focused beam of sound.

Catherine Palmer, director of audiology at the University of Pittsburgh Medical Center, said 140 decibels can cause immediate hearing loss. But there's no way to know if anyone was exposed to sounds that loud without knowing how far away they were, she said.

Putnam and public safety officials said the complaints prove the device worked as designed.

"You have to put your hands over your ears and cover them, and it's difficult to throw stuff," said Ray DeMichiei, deputy director of the city's emergency management agency.

Police said they used the device last Thursday to issue prerecorded warnings to disperse when hundreds of demonstrators, including self-described anarchists, without a protest permit held a march that threatened to turn violent.

Aware of concerns about the volume, police were careful to use it about 12 feet off the ground mounted on a tactical vehicle, so no individual would be directly in its path or too close to it, Assistant Chief William Bochter said.

"The only way anybody gets hurt is if the deterrent is on full blast and they stand directly in front of it," Putnam said.

A regional counterterror task force bought four of the devices from American Technology using $101,000 in federal Homeland Security funds, DeMichiei said. Because the amplified message was prerecorded, police could be sure the protesters heard exactly the instructions police desired and have confidence those in the back of the crowd could hear, Bochter said.

Such devices also have military and commercial applications. Putnam said the primary purpose is to transmit specific orders loudly and clearly.

They have been used against protesters overseas, and police in New York threatened to use one during demonstrations near the Republican National Convention in 2004.

He said the city of San Diego uses them to instruct people to leave large sections of beach after festivals. It has also been used in SWAT operations.

In military applications, it allows ships to hail approaching vessels and determine their intent, the company says. Cargo ships use them to tell pirates that they had been spotted. When the pirates know they have lost the element of surprise, they will not attack, Putnam said.

Putnam said those complaining about the device have probably exposed themselves to sounds nearly as loud at rock concerts, and for longer periods of time. Walczak, the ACLU attorney, isn't buying the analogy.

"People don't flee the front row of a rock concert. Why would they be fleeing here?" Walczak asked. "Because it's loud, it's painfully loud."