Of the many voices shouting for attention on the streets of Pittsburgh during the G-20 summit, one voice dominated with a controversial yet simple message: "By order of Pittsburgh chief of police, I hereby declare this an unlawful assembly. I order all those assembled to immediately disperse."

On the first day of the summit, Pittsburgh police unveiled the Long Range Acoustic Device, or LRAD, a sophisticated speaker system that can blast a clear, recorded dispersal order and be heard up to a quarter-mile away.

It also emits a high-pitched alarm sound that can drive even the most determined protesters to leave a scene.

Video and audio footage of the LRAD in action has circulated heavily on the Internet since the summit, and yesterday Pittsburgh police officials gave a demonstration of its capabilities to the media.

"This is a kinder and gentler way to get people to leave," said Raymond DeMichiei, city deputy director of the Office of Emergency Management and Homeland Security. "From what I've seen, I think it worked well."

Not everyone agrees.

Witold Walczak, legal director of the Pennsylvania American Civil Liberties Union, said his office is investigating claims that at least one person suffered hearing loss after being exposed to the LRAD.

Peter Shell, co-chair of the Thomas Merton Center's antiwar committee, called it a "dangerous weapon."

"I was definitely taken aback," he said of his first encounter with the LRAD when police used it to break up a non-permitted protest march through Lawrenceville. "It was very unnecessary escalation in police action."

The device's shrill setting was mocked by Jon Stewart, host of "The Daily Show" on Comedy Central, as the "latest in anarchist-stopping technology."

"Oh my God! Those anarchists are going to have to go like this!" he said as he covered his ears with his hands on the Sept. 28 program. "They're anarchists! ... Do you know what kind of music these people listen to? That cannon is probably their ring tone by now."

The LRAD can exceed 150 decibels, the equivalent of "peak" rock music, firearms or a jet engine, according to the American Speech-Language-Hearing Association.

Any sound greater than 80 decibels can damage hearing, the association's Web site says.

The LRAD's volume is controlled with an audio knob, and Pittsburgh police never raise it above the lowest level, Officer Stephen Mescan of the city SWAT team said after yesterday's demonstration in a parking lot at the North Side police headquarters.

With reporters standing 100 meters away, operators atop an armored SWAT truck played the same robotic voice that greeted hundreds of protesters during the summit with a direct order: "You must leave."

The full message, roughly two minutes in length, was repeated in English and Spanish. A swivel allowed police to point the 50-pound speaker toward confused motorists in traffic waiting to turn onto the West End Bridge.

Built by San Diego-based American Technology Corp., the LRAD is still a novelty among U.S. law enforcement agencies. It has been used by the Navy as a hailing device, and some cargo ships use it to confront pirates.

According to American Technology, the LRAD can also emit "bird distress calls" around airports to clear birds away from a plane's flight path.

In the months leading up to the G-20 summit, Pittsburgh public safety officials drew up a list of crowd control tools, including OC gas and beanbag rounds. Both were later used against protesters.

Mr. DeMichiei said the LRAD was seen as a safer alternative. With $101,000 in federal homeland security grants, the city and Allegheny County purchased four devices, which will be shared by law enforcement agencies operating under the umbrella of Western Pennsylvania's Region 13 Task Force.

Yesterday morning, SWAT officers deployed the LRAD to warn Beechview residents to stay in their homes during a standoff with an armed man on the 2300 block of Saranac Avenue. Police will likely bring it out in the future for events that attract large crowds or to broadcast important announcements during emergencies or evacuations.

"It is the best public address system you're going to find," Mr. DeMichiei said.

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