The "Mosquito" in Philadelphia

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Michaela Winberg, "Sonic Devices Target Teenagers In Philadelphia", NPR 7/5/2019:

WINBERG: If you look at the rec center building at Philadelphia's East Poplar Playground, you'll see a small beige speaker screwed into the wall. Every night at 10 p.m., that tiny speaker activates. And for eight hours, it plays nonstop. Here's what it sounds like.


WINBERG: Didn't hear anything? If so, it's likely you are not between the ages of 13 and 25. That's the age group this sound is targeted toward. As we age, some of the cells in our ears start to die off. So when we get older, we have trouble hearing higher-frequency noises like the one that this device plays.

Philadelphia resident Lamar Reed is 17, and he hears the noise loud and clear.

LAMAR REED: It's so loud. Like, it can – like, what if it damages our ears or anything like – something like that?

WINBERG: It's called the Mosquito, and it's an acoustic deterrent device, technology used to keep humans or animals away from a designated area. It's usually used by law enforcement or the military. The Mosquito was manufactured by Vancouver-based Moving Sound Technologies. Michael Gibson is the company's president and says he has worked with about 20 parks departments in cities around the country to install his devices.

Here's a clip including the "soundbite of static":

And of course it's not like "static" at all (which M-W defines as "noise produced in a radio or television receiver by atmospheric or various natural or man-made electrical disturbances", and sounds something like this), but rather a pure tone at 15 kHz:

(Though maybe there's an extended meaning in radio-land, something like "anything that's not speech or music"?)

Anyhow, Lamar Reed's comment is right on target, because one of the main reasons that "As we age, some of the cells in our ears start to die off" is that our ears are damaged by noise exposure.

The Facebook comments are also interesting, suggesting that some people older than 25 can also hear these sounds:

In my 30s, and I heard it. Randomly proud of my ears. They also have this sound at the grocery store to keep birds from nesting. I just try to get inside as quickly as I can.

I'm 47 and hear it clearly as an awful high pitched irritant! And from the comments, it's obvious that many people of varying ages hear the sound; it is not isolated to young ears! What about the insects, birds and animals that rely on their senses as well as park space in urban environments? I don't understand how this has passed environmental impact evaluation :(

I’m 38 and I heard it! Yay for good hearing.



  1. Peter B. Golden said,

    July 6, 2019 @ 6:46 pm

    My 7-year old granddaughter heard it.

  2. S Frankel said,

    July 6, 2019 @ 7:05 pm

    I'm 54 and had to rip my headphones off – didn't expect it to be so loud. I know some people 10 and maybe 15 years older than I am who can also hear high-pitched sounds that they're not supposed to be able to hear.

    What we have in common is that we play harpsichord and clavichord and we have to tune our instruments. Tuning by ear involves listening to high harmonics, and it's something we have to do often. Presumably our cilia deteriorate just like everyone else's, but maybe our brains learn to compensate somehow?

  3. Laura Morland said,

    July 6, 2019 @ 7:06 pm

    Televisions used to make a sound (presumably) in this range. When I was a kid growing up in the 60s, I realized at some point that my parents couldn't hear the high-pitched sound that the TV made when it was on with the sound turned off. (Presumably it made that sound continuously; it was simply masked by louder sounds in a normal range.)

    I used my parents' "old ears" to my advantage… whenever I heard one of them coming down the hall, I'd quickly turn off the sound and image, so they wouldn't realize that I was "sneaking" TV after bedtime. It worked 100% of the time. I could hear the high-pitched sound the TV was making — even several feet away, through a closed door — but they were immune.

    (Why not just turn off the TV? Because in those days televisions also emitted a very bright white light when they were turned off. It would last several seconds, first filling the screen, and then reducing to a small point in the center. Raise your hand if you remember that feature!)

  4. Joe Fineman said,

    July 6, 2019 @ 8:01 pm

    Laura Morland: That was the flyback signal that told the CRT to start a new line in the image. Google reveals that it was 15734 Hz. You weren'r supposed to hear it, but the signal was also fed into a transformer to generate high voltages for various purposes. As the TV set aged, the transformer got shaky & vibrated at the flyback frequency. In my youth, I heard it quite a bit — particularly from the TVs in bars, which were often pretty old. In the flat-screen age, of course, that is all ancient history, as is my auditory sensitivity at 15734 Hz.

  5. Andrew Usher said,

    July 6, 2019 @ 9:41 pm

    I can certainly hear it, though I did not at first due to the low volume I normally have my speakers at; I can also hear the sound on Wikipedia's page, said to be 17.4 KHz. I know roughly my ears' sensitivity to high frequencies, as I have tested myself many times – unfortunately not with the same device or program. I have not been able to notice any deterioration over the past 30 years, since the first time I tested. I avoid exposure to loud noise as much as possible, though, which probably accounts for my retaining good acuity, not just at the high end but at all frequencies.

    I do not know how loud this device actually is in practice; the Wikipedia page gives numbers but they are meaningless without a distance at which the measurement was taken.

    The interesting thing is that at still higher frequencies my threshold of hearing exceeds my threshold of pain; that is, I can feel the pain in my ears before hearing the sound as such. The range in which I have found this is 18-20 KHz, the latter reaching the limit of volume producible with any speakers I have. Presumably all people with normal hearing have such a frequency; audible sensitivity falls off (for everyone) rapidly starting at ~14 KHz, while pain sensitivity probably doesn't very much.

    I do not recall having ever heard the flyback frequency from a TV, though I probably did, but I do know that I have heard similar frequencies from other electronics. I'm pretty sure it was chosen to be high enough not to be obtrusive to hearing normally.

    k_over_hbarc at

  6. Andrew Usher said,

    July 6, 2019 @ 9:46 pm

    And this 'static' was probably just the same kind of loose usage from the media we're familiar with in linguistic terminology; I seriously doubt there's any other meaning that would include pure sine waves.

  7. Gregory Kusnick said,

    July 6, 2019 @ 10:16 pm

    Thermal noise endemic to all electronic circuitry is arguably a "natural or man-made electrical disturbance", but I'd be inclined to call it simply "noise" rather than "static".

  8. Andrew Usher said,

    July 6, 2019 @ 10:24 pm

    But in many receivers 'static' _is_ the inherent thermal noise amplified (the agc being all the way down) until it becomes detectable. I agree the electronic engineer would call it 'noise', but the user doesn't care where it comes from – white noise is white noise, and generally called 'static' in that context.

  9. Philip Taylor said,

    July 7, 2019 @ 3:13 am

    There is a very clear tone-burst between 8.2 and 10.4 seconds, of which I can hear nothing at age 72, but it is worth noting that it is about 6dB down on the peak level of the audio narration. See screenshot.

  10. Philip Taylor said,

    July 7, 2019 @ 3:14 am

    Sorry, URL disappeared from that. It should have read "See screenshot" (

  11. Philip Taylor said,

    July 7, 2019 @ 3:23 am

    Sorry, screenshot disappeared from that message, as did my follow-up which tried to add it. Trying again; The last part should have read "See screenshot" (

  12. maidhc said,

    July 7, 2019 @ 4:45 am

    It's stupid to put something on the internet and then say you didn't hear it because you're old.

    Whether or not you can hear something on your computer depends mostly on what kind of speakers you're using. S Frankel's headphones can obviously reproduce the frequency in question. But if you had some cheap low-end speakers, they might not do such a good job. It doesn't really have to do with how old you are.

    High-end hearing drops off with age, but it doesn't go immediately to zero once you hit 30. It just gradually gets less sensitive.

    Most people make very little use of their full hearing ability even when they are young, but people who do things like tuning harpsichords (as in S Frankel's example) are much more aware of what they hear. But it might be the case that as they get older it becomes harder to tune harpsichords when there is a lot of traffic noise outside, for example

    This topic shows up regularly every few years. Often it involves people selling 20 KHz audio oscillators at truly ridiculous prices.

    When I was in high school we did a lesson on this topic. At that time I could hear.maybe 22 KHz (of course this would have to be adjusted according to the listening situation). But there was one kid in our class who could hear up to about 25 KHz. He said when he was out at night he could hear bats.

    If you want to get teenagers to go away, there is a well-known and inexpensive method to do that–play classical music. These people like Moving Sound Technologies are just scam artists, selling things that don't work any better than the low-cost solution at inflated prices backed up by a lot of pseudo-scientific hype.

  13. AntC said,

    July 7, 2019 @ 7:53 am

    In one of the local shopping centres here that was plagued by the yoof, they play light classics: Strauss waltzes, Brandenburg concertos, Mozart/Haydn symphonies …

    Certainly has dispersed the yoof. They're now plagued by Hell's Grannies ;-)

  14. Martha said,

    July 7, 2019 @ 11:09 am

    Whenever they try to use classical music to get rid of teenagers, it just makes me think of A Clockwork Orange.

  15. Andrew Usher said,

    July 7, 2019 @ 11:19 am

    Yes, your reproduction equipment has some effect. Headphones are generally good – but speakers are OK also. Unless they're filtered out (which there's no reason to do), very high frequencies will be reproduced by speakers at a sufficient level for this demonstration – there's no physical way for the response of a speaker to fall off that rapidly. As I did, simply turn your volume all the way up if you think you need compensation.

    These products do what they say they do, and have real science behind them, so you can't call the Mosquito a scam. Of course they over-hype it, but that's what all companies do when selling their products.

    I already mentioned that the apparent frequency limit of hearing, for anyone of any age, will be significantly affected by volume (and distractions), up to the level where it becomes painful. 22 and 25 KHz are not absurd at sufficiently high levels (that normally can't be attained by a computer/speaker setup); no one could hear them at 'quiet' levels. A study I read found that some subjects heard 28 (but not 30), at levels around 115 db, which I would surely find painful.

    I certainly grant that training makes a big difference in terms of how well you interpret what you hear. But it can't change what your ears are physically capable of.

  16. Gregory Kusnick said,

    July 7, 2019 @ 11:49 am

    Andrew: The NTSC flyback frequency is just the product of the vertical resolution (525 lines) and the frame rate (~30 Hz), so I don't think there was any deliberate intent to fix it at an imperceptibly high audio frequency. That outcome seems more serendipitous than planned.

  17. BobW said,

    July 7, 2019 @ 2:59 pm

    I won a small bet by when I worked at JC Penney Product Service as a consumer electronics repairman by being able to tell if a TV set was turned on in the next room, just from the flyback whine. Since I am in my mid-sixties now that ability is probably gone, but with the demise of CRTs there is no easy way to check. I do remember the disappearing dot in the old tube-based (valve-based for Brits and others out there) sets. And the long warm-up times. Ever change channels with a pair of vice-grips?

  18. Viseguy said,

    July 7, 2019 @ 6:09 pm

    "Flyback whine"! Thank you, BobW. I remember it well, along with the slowly disappearing dot, which as a preschooler I insisted be allowed to vanish completely before my dad carried me off to bed. Those were the days when they did TV right — a nicely-finished piece of heavy furniture, not a goddam glass rectangle that you can put in your back pocket. I dunno what the world is coming to…. But seriously, the idea that classical music is an effective teenager repellent is profoundly depressing.

    Back on topic: I couldn't hear that tone for squat. I'm 68.

  19. scout said,

    July 7, 2019 @ 10:47 pm

    Has this clip been converted through a lossy format? Mp3 and others generally clip off the high end above 14khz, so what you're hearing might be aliasing. If this was broadcast, does FM radio allow transmission in the 15khz band?

  20. Andrew Usher said,

    July 7, 2019 @ 11:17 pm

    Gregory Kusnick:
    When the TV standard was set, there werer other proposals for the number of lines, in particular 441. It's not unlikely an objection to that was the greater possibility of nuisance sound at the horizontal scan frequency. Even if it wasn't in America, it probably was considered in Europe – they set their frequency at almost exactly the same (625*25 = 15,625), even though there was no need for more scanlines. But I'm not sure and haven't read anything definite about it. Nonetheless, had America chosen 441 lines, or Europe 525, TVs could easily become unwatchable without strong damping of the flyback.

    I don't understand the last comment – the high-pitched tone is certainly there, whatever format it's in. It is annoying the sound files here are not downloadable, so I can't take a look myself. And it certainly has never been broadcast through 'FM radio'.

  21. Keith said,

    July 8, 2019 @ 3:05 am

    These mosquito devices have been around for quite a long time.

    I first remember reading or hearing about them in the UK back in around 2010, I think, though I may well be mistake; below is a link to an article in the Independent from June 2013.

  22. Philip Taylor said,

    July 8, 2019 @ 3:16 am

    Andrew, why do you say (in re the UK's choice of 625 lines v. the US's choice of 525) "there was no need for more scanlines" ? More scanlines = higher image quality, whence today's 1080P and 4K standards.

    There is also the ?fixed? overhead of approximately 50 scan lines required to allow adequate time for vertical flyback, an overhead that was later used to implement teletext in much the same way that SMS piggybacks on mobile telephony protocols today.

  23. Trogluddite said,

    July 8, 2019 @ 1:22 pm

    I can confirm Keith's comment about the UK: at least five years ago, the village shop near where I lived at the time had such a device installed, with the intention of keeping groups of schoolkids from hanging around outside. It was got rid of pretty quickly once they realised how many customers it was keeping away, myself included.

    My high-frequency hearing has always been good for my age; but has been a rather mixed blessing, as I always found the noises from TV scan coils and ultrasonic pest/pet deterrents etc. very distracting and irritating at the least, and sometimes rather uncomfortable. Hearing bats occasionally was quite nice, but it seems that there's generally not a lot going on up there that human brains can make much sense of!

    "Static" to mean audio or video noise was common parlance here in the UK when I was growing up. I'm less certain whether it's so common among younger people here who didn't grow up tuning into radio and TV stations manually – though I suspect that it would be less well known to them.

  24. Trogluddite said,

    July 8, 2019 @ 1:26 pm

    PS: I've always thought that "static" for noise derives from the similarity with the crackling of static electricity. I have no idea whether that's something I was taught many moons ago or just an intuitive metaphor, nor how true that might be.

  25. Gregory Kusnick said,

    July 8, 2019 @ 2:22 pm

    Trogluddite: AM radio static doesn't just sound like the crackling of static electricity; it actually is the radio-frequency noise produced by electrical discharges in the atmosphere.

  26. Chris C. said,

    July 9, 2019 @ 1:26 am

    I'm 56 and I could hear it. I had to use high-quality headphones with the volume turned way up, but I could hear it. But at that point, it was exceedingly unpleasant.

    This is a notable deterioration from when I was in my 30s and could be seriously annoyed by the squeal of a glitchy CRT monitor, which no one else in my office could hear.

  27. Rube said,

    July 9, 2019 @ 7:05 am

    FWIW, neither my wife nor myself (59 and 60) could hear it, but our 18 year old son heard it, said "of course" he could hear it, and found it quite unpleasant.

  28. Andrew Usher said,

    July 9, 2019 @ 6:44 pm

    Chris C.:
    Yes, that confirms what I said about the threshold of pain. Of course 'pain' when it comes to sound is not complete objective, but I imagine the spread would not be too wide (obviously excluding people objecting to the nature of the sound rather than its volume). But yes, many more people can hear this sound, when played at levels sufficient to be annoying, than just the young – that's one reason I don't believe they'll ever become popular.

    This device is called the 'Mosquito', a name chosen, presumably, because of the similarity of effect rather than of sound, because real mosquitoes don't sound like this – in fact, I'm not sure their buzz even has a pitch.

    Philip Taylor:
    It was analog TV with a fixed bandwidth. More vertical resolution directly meant less horizontal resolution. The decision was by no means obvious, and no, there is not a fixed number of scanlines between frames (unless the standards people make it so) – the actual retrace is fast compared with the frame rate. There was a time before digital encoding, and that should be thought of before posting an instant opinion.

    All I was saying is that it seems unlikely to be a complete coincidence that both standards chose almost the same horizontal frequency, and one just high enough to prevent nuisance from sets in working order. (Our sensitivity drops off most steeply between 14 and 16 KHz.)

  29. Philip Taylor said,

    July 10, 2019 @ 5:40 am

    Andrew ("There was a time before digital encoding, and that should be thought of before posting an instant opinion"). The "time before digital encoding" is the time to which I was referring; anything post-digital is surely irrelevant to the topic under discussion, since to the best of my belief the ability to handle digital encoding was never present in CRT-based televisions. As regards the number of scan lines between frames, Wikipaedia says "In analogue, 49 additional lines without image content are added to the displayed frame of 576 lines to allow time for older cathode ray tube circuits to retrace for the next frame[2], giving 625 lines per frame. ". Whilst WP is by no means infallible, its analysis in this respect is an accurate reflection of reflect my own beliefs.
    [2] The 625-line television standard was introduced in the early 1950s. After tracing a frame on a CRT, the electron beam has to be moved from the bottom right to the top left of the screen ready for the next frame. The beam is blanked, no information is transmitted for the duration of 49 lines, and circuitry relatively slow by modern standards executes the retrace.

  30. Wanda said,

    July 11, 2019 @ 12:45 pm

    I'm 35, I could easily hear that clip, and I've been hearing such devices all my life- at least since I was 6 or so, at certain high-end grocery stores that my parents used to take me to. I hate these devices, especially when they are at places where young people might need to spend time. How is a teenager supposed to disperse from a train station when they need to catch a train?

  31. Wanda said,

    July 11, 2019 @ 12:45 pm

    In any case, as more people learn about the importance of protecting their hearing, the range of people who hear and are bothered by these devices is going to expand. There is nothing natural or inevitable about the degeneration of the cilia. In societies where there is no amplified sound or unnatural loud noises, even the elderly can perceive these noises. (I bet that's the deal with the harpsichordists on here- harpsichord concerts are not particularly loud, so they keep their hearing.)

  32. Andrew Usher said,

    July 12, 2019 @ 6:55 pm

    Philip Talyor:
    You're not an expert on television, clearly, why appear to be? I, of course, knew that TV was before digital encoding, and that was the very point. In that time there was a 1:1 trade-off between horizontal and vertical resolution, and it's unclear that increasing the latter was a good thing – but it did get the flyback frequency out of the problematic range.

    And, without consulting Wikipedia, I know there are reasons to have scan lines between frames, but not necessarily a fixed amount. The TV performs (as it must) horizontal retrace in a few microseconds; why must it take milliseconds for the vertical? It does not, and the American standard, despite being older, never used as many as 49 lines' spacing. Indeed, in the early days, that number didn't need to be standardised at all – people adjusted their sets so the picture filled the screen, and it wasn't really important what was in the part off screen. Only, again, with digital encoding, did we finally have to decide on 480 and 576 picture lines (somewhat less than was technically possible).

    But is there really any point? Everything you say in animated by your vigorous dislike of American and everything American, including your apparent failure to understand anything that might lead to the contrary.

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