Its effects have been likened to standing in front of a jet engine -- a blast of amplified sound capable of inducing headaches, panic, and potential hearing loss.
This is the LRAD, or Long Range Acoustic Device, which can emit a 150-decibel beam of sound and has become increasingly popular as a crowd-control device in the United States and around the world.
The LRAD first made headlines when police in the U.S. city of Pittsburgh, Pennsylvania, used the device to repel antiglobalization demonstrators protesting the G20 summit in 2009.
A video from the event
shows protesters covering their ears and backing away as the truck-mounted LRAD, which resembles a satellite dish, emits a high-pitched noise, similar to a car alarm.
The LRAD can also be used to transmit spoken messages across long distances. In Pittsburgh, police used the LRAD to warn protesters
to evacuate the city streets surrounding the summit site.
The LRAD was developed after the 2000 attack on the "USS Cole," a U.S. Navy vessel, in Yemen.
Suicide bombers were able to approach the vessel in a small boat, while navy crewman had no way of communicating with the passengers or determining their intent.
According to Robert Putnam, the head of investor and media relations for the LRAD Corporation in San Diego, California, the LRAD is now frequently used at sea and to transmit a targeted message over a large distance.
"With our largest devices we're able to reach up to 3.5 kilometers away, over land, water, and almost any type of environment or condition,” he says. “And we're able to use an alarm tone to get people's attention and then speak to them in their own language to [warn them to] quit coming closer. If they continue to come closer then there are other escalations of force that military, commercial security, or other entities can use.
“But the whole intent of LRAD is to be able to use it to determine the intent [of a potential attacker] at a distance, with the hope of using communication to resolve uncertain situations peacefully and, more importantly, to save lives on both sides of the Long Range Acoustic Device."
The LRAD, which is sold mainly for military, law-enforcement, and commercial-security purposes, can be used in search-and-rescue operations and as a deterrent to keep birds away from airport runways.
But it's the LRAD’s use as a crowd-control device that has gained it most of its publicity, with some critics referring to it as a “sound cannon.”
The LRAD, which is not categorized as a defense article and requires no U.S. export license, has been sold to 60 countries worldwide, including Azerbaijan, Georgia, and Poland. The LRAD ranges in price from $5,000 for a basic handheld model to its most expensive model that sells for between $100,000 and $190,000.
Civil liberties unions in both Canada and the United States have expressed concern about the use of the LRAD, which they characterize as “military-grade” equipment, by police.
The LRAD can reach decibel levels as high as 162. For comparison, a normal conversation is usually 60 decibels, while a lawn mower can reach to 90 decibels. A level of 130 decibels is typically considered the average pain threshold for most humans.
The beam of sound is so precise that a person standing behind or next to an LRAD device can hear almost nothing. But Putnam maintains that the LRAD can do little damage even to those people targeted by the beam.
"It gets your attention, but it does nothing to you,” he said. “And you'd have to be in very close proximity for it to do any kind of issues as far as to someone's hearing. As with any loud sounds, you cover your ears with your hands and you instantly drop the sound level. So that even with our largest device, you could be standing directly in front of it with your hands covering your ears and you'd suffer no hearing damage and it would cause no injury to you.
“There have been some reports in the press who have tried to turn it into a sonic cannon or something like that, and that is not what it is. It really is a long-range communications device. I've done it personally several times."