If you’re 18 years old or over, you probably have a condition called presbycusis. But don’t be concerned. It is very, very common among those of us who are, legally, adults. And it is also not a very big deal. Presbycusis is the scientific name for “age-related hearing loss,” and it simply means that we don’t quite hear as well as we did as teens — but we can still hear fine. For the most of us, by the apparently ripe old age of 25 (yes, twenty-five), there is only one noticeable effect — we cannot hear very high pitched sounds which our younger selves would have picked up on.

For the makers of the Mosquito, this fact is the key to a business model.

The Mosquito, pictured above, is not a bug — at least not to the older set. It is an alarm system of sorts, one which emits a high frequency (17.4 kHz) pitch, one which the company claims is inaudible to most people over the age of 25, but audible — and irritating — to tweens and teens. The device can be used by shopkeepers (such as fast food joints) who want to rid themselves of loiterers of that age bracket, near public transportation where vandalism is common, etc. It is not without controversy, though. First, there’s a real question as to whether it works. A casual product test by WIRED in 2007 had mixed results, with tweens only showing a mild “annoyance” at the noise, and noted that people older than 25 could definitely hear the noise. But even if it does work, some believe that its use constitutes a human rights violation. As one UK watchdog group told the BBC, the Mosquito targets both innocent children as well as ne’er-do-wells: “There have been discussions locally and nationally on the legality of a device which does not distinguish between those causing nuisance or anti-social behaviour and those who do not.” There is pending litigation and/or legislation aimed at outlawing the Mosquito in the UK, Ireland, France, and Belgium, as well as at the European Union level.

But don’t cry too many tears for the tween and teen targets of the noise box — the kids may have the last laugh after all. As reported by Metro, some enterprising young adults have modified the Mosquito’s technology to work with cell phones. The children have turned their ringtones into the high-pitched noises which only they can hear, allowing them to take calls and text messages without alerting their (older) teachers.

Bonus fact : Mosquitos — the flying, biting kind — prefer Type O blood to other types, according to NYU’s ScienceLine.

From the Archives: Sounds From the Deep: More sounds which were hard to hear. But for different reasons.

Related: A giant, huggable mosquito. Eww.