It sounded like a clever way to deter vandals who had persistently plagued a Hastings park: The SonicScreen, a device that emits a high-pitched, annoying sound audible almost only to teenagers.

By switching it on after park hours, the theory goes, the city could discourage late-night loitering and vandalism by teens. The device would be the first of its kind in Minnesota.

But before the city has even placed an order for the equipment, some are already calling it age discrimination.

"Teenagers are not pests to be repelled," wrote David Moss, a leader of the nonprofit National Youth Rights Association, which sent a letter to the city protesting the idea.

Teens were targeted because police statistics show that they commit most vandalism, and the one vandal caught at the park was a teenage boy, said Hastings Parks Director Barry Bernstein.

"We don't want anybody there after 10 p.m.," Mayor Paul Hicks said. "I don't care how old you are. ... The message is: 'The park is closed.'"

The city's parks and recreation commission will resume its discussion Wednesday night about the SonicScreen and other ideas for deterring vandals at Cari Park, which has been sprayed with graffiti and even had some playground equipment burned.

The park is susceptible to vandals because it is surrounded by homes, affording no clear view to squad cars patrolling nearby streets. "The neighborhood is frustrated with past vandalism and is open to new strategies," Hicks said.

One alternative, bright lights, would bother residents, Bernstein noted. (The SonicScreen's range is only 75 feet, so people in nearby houses shouldn't hear it.)

Although wearing earplugs could block the screeching sound, Bernstein said vandals aren't known for planning ahead.

"It's a last-second decision," he said. "I don't think teenagers spend two weeks deciding how to trash playground equipment."

Bernstein said SonicScreen would cost about $9,000 and could be installed in a post of the new playground equipment, which would cost about $40,000.

Brian Faletti, who has two young daughters, lives by Cari Park and says something needs to be done about the graffiti and vandalism. He's not sure if SonicSreen is the answer, partly because of its cost and its lack of a track record in Minnesota. He wondered if the noise screen might be heard by adults walking their dogs in the area.

SonicScreen was unveiled in September 2009 by the Miracle Recreation Equipment Co. of Monett, Mo. Company officials said it is used in cities in Virginia, California, Missouri and Mississippi and in Europe and Canada.

'Unabashedly discriminate'

After news stories appeared about the idea, the National Youth Rights Association in Washington, D.C., sent Bernstein a cautionary letter. It said devices like SonicScreen "unabashedly discriminate on the basis of age." Moss noted that the group's complaint to the Washington D.C. Human Rights Office caused a similar system near a city subway to be removed last year.

Hicks said he has received an e-mail from a Washington, D.C., businesswoman involved with the short-lived screech device, called the Mosquito, in her city.

It was installed to deter loitering and crime near a subway stop. Although the sound level was set to deter all ages, a whirlwind of protests led to its removal. "Instead, we play classical music, which was highly recommended," wrote Paula McDermott. "It doesn't work."

Miracle Recreation's Mike Sutton said the device has two settings: One shrill sound at about 18 kilohertz is for teenagers and travels about 75 feet. The other setting is for all ages and carries about 100 yards, which might be heard in homes around Cari Park, he said. He described the noise as not painful, but "bothersome, like the sound of a dentist's drill."

Sutton said people's hearing varies, but generally youths can't hear the sound until they are 11 to 13. Human hearing begins to decline in the 20s, making the high pitch inaudible, he said. Nor does the sound affect animals, he added.

Moss disputes that, saying an audiologist told him dogs hear in the 10 to 20 kilohertz range.

"I don't see why we need to target specific groups, even if [teens] are the most likely to be engaged in the practice," Moss said. He said motion sensors that trigger lights or recorded warnings to order people to leave are better, nondiscriminatory solutions.

Kevin Lindsey, state Human Rights Commissioner, said that Minnesota has less broad protection for age discrimination than Washington, D.C. does.

But even with broader protection, the Hastings situation seems to be exempt because the device would be used only when the park is closed to all visitors, he said.

Basically, Lindsey explained, anyone doing something illegal, such as walking in the park after hours, would have no grounds to file a human rights complaint.

The parks commission will discuss Wednesday night whether to make a recommendation to the City Council about the device.