Can Strategic Sound Deter Loitering?

Noise probably doesn’t pop into your head as being a major public deterrent — unless you happen to live in an area with an excess of it. Noise pollution can cause problems with well-being and physical health, so it’s not a stretch to understand how noise could be used strategically for crowd control and even as a weapon.

One controversial example is a device known as the “Mosquito,” which is being used as a tool to deter loitering in city parks and playgrounds. Although the device emits a high-pitched ringing noise, it can only be heard by the target audience — teens and young adults that city officials hope to keep out of certain areas after dark.

How Noise Is Being Used as a Youth Repellant

Philadelphia is one U.S. city that’s installed the Mosquito, a small speaker-like device, in 30 parks and recreation centers.1 Their purpose is to deter youth from hanging around the areas at night by emitting an unpleasant, high-pitched noise.

According to their parent company, Moving Sound Technologies (MST), the sound is similar to the buzzing of a mosquito and, when set to 17KHz, can only be heard by people between the ages of 13 and 25 years.2

This is because as people age, they typically have a harder time hearing high-pitched frequencies. Generally, adults hear sounds in the 0.02 to 16KHz range (sound is measured in hertz (Hz), with one KHz being equal to 1,000 Hz),3 but it’s not a perfect science.

Data are scarce on whether the devices work to reduce loitering or vandalism, but anecdotal reports on MST’s website suggest the relatively innocuous devices are leading to fewer incidents in areas such as condominium stairwells.4 In Philadelphia, the noise makers operate only from 10 p.m. to 6 a.m. and work in concert with other antivandalism tools, including security cameras, security staff and fences.5

Is Targeting Teens With Noise Ethical?

Part of the controversy over the Mosquito stems from the fact that some people living around the parks where it’s being used say they can hear the ringing. Mary Kate Riecks, who is 27 years old — outside of the device’s targeted age range — told NPR that she can hear the noise from a Mosquito a few blocks away:6

"It almost is more like a feeling than a sound. It's kind of in the back of your head … At least for me, it gives me a headache if I'm near it for too long. So I usually skip around this block or walk very quickly down it."

There is also concern that young children, including those unable to express their discomfort, can hear the noise, and the National Youth Rights Association suggested the devices are a form of age discrimination. The city of Washington, D.C., which had installed the devices in the Gallery Place Metro station in 2010, removed them due to discrimination concerns.7

The United Nations Committee on the Rights of the Child also suggested the Mosquito and similar devices may violate children’s rights. They’ve since been banned in certain public spaces in several England counties.8 Even in Philadelphia, their use is controversial. City Council member Helen Gym called them “sonic weapons,” stating, as reported by NPR:9

"In a city that is trying to address gun violence and safe spaces for young people, how dare we come up with ideas that are funded by taxpayer dollars to turn young people away from the very places that were created for them?"

Also at issue is whether the sounds could produce harmful effects, although MST says no long-term side effects occur.

“The Mosquito has been tested by various US, Canada, United Kingdom and European Union government agencies, environmental groups and human rights groups and has been found to be completely safe — there is no risk of long-term hearing damage from The Mosquito,” according to MST, which notes the devices are designed to run at 5 decibels above background noise levels.10

As for their potential to interfere with human rights, Simon Morris, director of Compound Security, defended their use, telling CNN:11

"We're all parents as well … The Mosquito was born out of our children suffering because they were attacked or assaulted at local shops by older kids. We've never had the intention of curbing anybody's rights. People have the freedom to walk away from the sound and the sound is highly targeted into a very small area."

Music Used as Control Tools

Aside from the high-frequency noise being emitted by the Mosquito, other devices emit sounds in the form of music, also as a tool for control. In West Palm Beach, Florida, songs including “Baby Shark” are played from loudspeakers to deter homeless people from sleeping near an event center.12

Classical music is also used as a crime deterrent. In London, when music was played in tube stations, it’s said that robbery rates dropped by 33%, while verbal and physical abuse incidents also declined.13 In Germany, atonal music, which lacks harmony and can sound like random noise, was going to be played in train stations to deter loitering, but the idea was abandoned following widespread public criticism.14

Ultrasonic sounds, with frequencies of 20 kHz or more, also exist,15 and sonic attacks have been rumored to have occurred.16 This frequency is higher than most adults can hear, but it’s thought that some people may be sensitive to adverse effects from exposure, including headaches, nausea and tinnitus, or ringing in the ears.17 Tim Leighton, a professor of ultrasonics at University of Southampton, told CNN:18

"In the 1940s people started complaining about ultrasonic sickness, with symptoms like headache, excessive fatigue (and) irritability. The first legal case was in 1948 … A high frequency above 20 kilohertz, if you can hear it, will affect you for sure.

It can affect your concentration, your ability to do tasks, give you headaches (and) make you uncomfortable. We haven't been allowed, under our ethical guidelines, to look for stronger effects. It's almost likely that stronger signals will lead to a temporary, perhaps even permanent loss of hearing. But we can't test for that because it would be unethical for us to expose people to that."

How Noise Pollution Affects Your Health

Noise pollution, which is defined as “unwanted or disturbing sound,” affects millions of people, leading to adverse health effects. Noise-induced hearing loss is one of the most obvious effects that can occur from exposure to persistent or loud noise, but other unexpected health effects also occur, including:19

  • High blood pressure
  • Stress and related illnesses
  • Speech interference
  • Sleep disruption
  • Lost productivity

Further, according to research published in Environmental Health Perspectives, long-term exposure to traffic noise may account for approximately 3% of coronary heart disease deaths (or about 210,000 deaths) in Europe each year.20 How, exactly, does noise harm your heart?

One of the key ways is by elevating stress hormones such as cortisol, adrenaline and noradrenaline, which, over time, can lead to high blood pressure, stroke and heart failure. One review of research showed that “arousal associated with nighttime noise exposure increased blood and saliva concentrations of these hormones even during sleep.”21

Deepak Prasher, a professor of audiology at University College in London and a member of the WHO Noise Environmental Burden on Disease working group, states:22

“Many people become habituated to noise over time… The biological effects are imperceptible, so that even as you become accustomed to the noise, adverse physiological changes are nevertheless taking place, with potentially serious consequences to human health … Taken together, recent epidemiologic data show us that noise is a major stressor that can influence health through the endocrine, immune, and cardiovascular systems.”

The impact can be significant. Among women who judge themselves to be sensitive to noise, chronic noise exposure increased the risk of cardiovascular mortality significantly.23

Using Noise for Good

Noise can be used to promote your health, just as it can be used against it. One example of positive noise is pink noise, which contains frequencies from 20 Hz to 20,000 Hz, just like white noise, but the lower frequencies are louder and more powerful than the higher frequencies (white noise, in contrast, has equal power in all of its frequencies).24

Research published in Frontiers in Human Neuroscience revealed that listening to pink noise could improve sleep and memory among 60- to 84-year-olds, a population that tends to have reduced slow wave sleep, or deep sleep, compared to younger individuals.25 While spending the night in a sleep lab, participants listened to pink noise one night and no noise the next.

Notably, the pink noise was played in bursts to match the timing of participants’ slow wave sleep. Not only did the pink noise enhance slow wave sleep, it also was linked to better scores on memory tests.

The participants scored about three times better on memory tests the morning after listening to pink noise in their sleep.26 Pink noise, for reference, is a gentle sound similar to that of rushing water or wind blowing through leaves on a tree.

How to Protect Yourself From Nuisance Noise

The upside to devices like the Mosquito is that you should (in theory at least) be able to avoid them by moving away from their targeted locale. If you live in a very noisy area, such as near a highway or airport, you may want to consider moving.

If that’s not an option, consider adding acoustical tile to your ceiling and walls to buffer the noise. Double-paneled windows and insulation can also help. At the very least, you can sound-treat your home by adding heavy curtains to your windows and rugs to your floors, and by sealing air leaks.

If noise is an issue only occasionally, sound-blocking headphones can eliminate such disturbances. You can also add beneficial noise to your home. Pink noise CDs are available, or you can also simply turn on a fan in your bedroom to block out noise disturbances and instead take advantage of this beneficial type of noise.

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