ROCKAWAY TOWNSHIP, N.J. - Whether it's fingernails grinding across a chalkboard or a crying baby, engineers at the Picatinny Arsenal are determined to find a noise so irritating that it disables the enemy.

The Morris County facility has turned out ammunition since the Revolutionary War, and the sound of rifle fire can still be heard at the Army's research and testing facility.

But Picatinny is also known for developing nonlethal weapons such as sponge grenades, rubber bullets and sticky foam, and arsenal engineers now say they are about six months to a year away from developing a useable acoustic weapon.

The idea is to fire skull-thumping sounds that drive adversaries from buildings or caves or to break up unruly crowds.

"Acoustics is kind of like a tooth ache, if it's done correctly," Peter Dotto of military consulting firm M2 Technologies told The Star-Ledger of Newark. "The bones in your skull...start vibrating, so you can't concentrate on anything else."

The arsenal has tested several dozen sounds, but found one of the most effective is a crying baby. Engineers have even made the sound more annoying by recording the cry backward so the listener won't become used to it and block it out.

"We're looking for sounds that are aversive, things that are the universal mother-in-law," a Picatinny engineer said. "No matter where you go in the world, a baby's crying will bring the same response from people. It mean's something's wrong."

They also envision troops using recorded sounds and an emitter to make it sound as if a helicopter is hovering about 100 yards away or machine gun fire is breaking out behind a tank.

The arsenal has partnered with ATC, a San Diego electronics firm, to make the ideas a reality.

While sound waves normally scatter in all directions, ATC has discovered a technique to aim a narrow column of sound, like a beam of a flashlight. Only the person in the sound's pathway hears it.

Army engineers say the technology could be used to saturate an area in aversive sound for things like crowd control. Or it could be used to talk directly to the leader of a group without anyone else nearby hearing.

The aim of the nonlethal technology is to limit injuries and property damage.

"As we do more peacekeeping missions, fighting wars where the political side effects are important, we have to be very precise in who we hit and how we affect our victims," said Loren Thompson of the Lexington Institute, a nonpartisan think tank in Virginia.

Yet there is concern that the weapons could be dangerous. Testing continues on technology to see how people react to sounds that can reach twice as loud as a jet engine, said Del Kintner of American Technology Corp., a California electronics company working with Picatinny.

"What if a person has a pacemaker? What if a person has a flaw in the ear canal? It might kill him," Kintner said. "Is it really nonlethal? All we know is it's very uncomfortable when you're in the beam, it disorients you. If you keep it up, it will really hurt you."

History shows that blasting the enemy with sound is not always effective.

U.S. Troops in Panama blasted Manuel Noriega with rock music in 1989, including songs such as "Nowhere to Run" and "I Fought the Law," in hopes of driving the general from inside a Vatican embassy.

Noriega was unmoved.