This is DAY TO DAY. I'm Noah Adams.

In a few minutes, creating a temporary city for disaster victims.

But first, how can law enforcement agencies control crowds and stop troublemakers without endangering the innocent people? Several US police departments are now exploring a new method that could replace tear gas and rubber bullets. It is sound. DAY TO DAY's technology contributor Xeni Jardin returns now with this report.

XENI JARDIN reporting:

It's a hot morning at Edwards Air Force Base in Southern California. About a dozen guests from military and law enforcement agencies stand in the shadows of three towering flat black panels up to 10 feet tall. Out of them blasts a duo between Frank Sinatra and Bobby Darin.

(Soundbite of "Mack the Knife")

Mr. FRANK SINATRA: (Singing) My man, Louie Miller...

Mr. BOBBY DARIN: (Singing) He split the scene, babe.

JARDIN: This device is more than a fancy speaker; it's MAD, a magnetic acoustic device that can broadcast a targeted beam of sound for more than a mile. It's built by California-based HPV Technologies. Testing the device from a mile away, we can still hear every word of "Mack the Knife."

(Soundbite of "Mack the Knife")

Mr. SINATRA: (Singing) Old "Satchmo" Louis Armstrong, Bobby Darin...

JARDIN: Representatives of the US Army, Marines and the UK Home Office are here for the demonstration. You may wonder why they're interested in technology that can throw Frank Sinatra's voice for a mile. Commander Sid Heal of the LA Sheriff's Department says his office is considering it for a variety of purposes.

Commander SID HEAL (LA Sheriff's Department): The first way is the conventional idea of replacing the normal hailing devices, where we can talk to people that need to be rescued, where we have crowd and riot control. Then the other way, though, that the human brain is sensitive to certain frequencies, and because we can recreate those frequencies quite easily, we can simply broadcast things that are irritating enough that will people will avoid them.

Mr. VAHAN SIMIDIAN (HPV Technologies): The easiest way for me to explain it to you is it's like a laser of sound.

JARDIN: That's Vahan Simidian of HPV. He explains that magnets inside those devices can convert electrical pulses into sound waves and aim them precisely for thousands of feet. The unit blasting us today is just a prototype, but Simidian says sonic technology has already proven useful for US troops in war zones.

Mr. SIMIDIAN: So that if they want to speak or alert somebody, let's say in Iraq, that's coming too close to a checkpoint and they want that person to stop but they need acknowledgement, they can point it right at them, talk to them and tell them, `Take another step forward, you're in our firing range. You're done.'

Unidentified Man #1: You are in a Navy vessel exclusion zone. Reverse course immediately or I will fire upon you. I say again...

JARDIN: When you're at close range, the sound from these devices can be terrifying and painful. A smaller device is being demo'd here today for use at shorter distances called LRAD. It's made by American Technologies, or ATC. About 300 LRADs, or long-range acoustic devices, are already in use mostly by the Department of Defense. A.J. Ballard of ATC radios his assistant a quarter-mile away and tells him to turn the machine on.

(Soundbite of high-pitched noise)

JARDIN: Tough military guys standing next to me grab their hands to their ears and duck reflexively. The sound is intense.

Unidentified Man #2: We got the point.

Unidentified Woman: That will be the last time I play the tone. I trust that you found the tone to be very effective at gaining your attention and also difficult to listen to.

JARDIN: Both HPV and ATC are donating some of their devices to authorities working in areas affected by Hurricane Katrina to supplement battered communication systems. Commander Heal from the LA Sheriff's Department says they're considering adding sonic devices to their array of non-lethal weapons.

Cmdr. HEAL: We've got everything. You name it, we've got it; pepper balls, pepper spray, menodinox(ph), sponge grenades...

JARDIN: Commander Heal finds sonic devices attractive for crowd control. His police could instruct and possibly repel crowds without getting too close. He and other American police officials hope they have better luck with sonic devices than other non-lethal weapons such as TASERs and pepper guns that have caused fatalities.

That's not to say that sonic weapons can't do harm. Earlier this year in Jerusalem, the Israeli army used a device nicknamed `the Scream' to scatter protest groups. `The Scream' sends out noise at frequencies that affect the inner ear creating dizziness and nausea and can cause hearing damage. Still, A.J. Ballard says that as far as weapons go, the sonic devices cause minimal damage.

Mr. A.J. BALLARD (ATC): You can get a headache, you can get a pretty good headache, but again, nobody gets killed here. Right? I mean, nobody takes a tear gas can right between the eyes.

JARDIN: The cost of these sonic gadgets--15 to $100,000--may put them out of reach for smaller law enforcement departments right now, but if police in New York City and Boston, who've already placed their orders, have success with devices, you may be hearing a lot more from them soon. For NPR News, I'm Xeni Jardin.

ADAMS: More coming up on DAY TO DAY from NPR News.

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