Is this what you are talking about and if it is,I don't think its meant for real mosquitoes. It's a device that uses high-frequency sound to stop teenagers congregating outside shops,schools and railway stations in UK. Test your hearing by playing the frequencies below - a copy and paste from Google. I've done the test & I'm afraid to say that my ears are 'effed'!!! Could be the matatus loud music or my age which I've refused to accept but damn!!! I need hearing aid ASAP or I'll be shouting WHAAT? soon What is the Mosquito Ringtone? The short version,A tone outside the audible range of hearing for most people over the age of 30. This means that you can get phone calls and receive text messages in class or school without teachers hearing it. For more in-depth information on how the mosquito ringtone works,please see the Mosquito RingTone FAQ. For information on how to get the ringtone on to your phone,see our Mosquito Ringtone how-to Guide. + = A ring tone teachers & parents can’t hear! Hence exam cheating!! Download The Mosquito Ringtone! Get the REAL ultrasonic ringtone for your cell phone now. You can hear it,but they can’t! Click Here Frequency Age Range Play / Download 8khz Everyone 10khz 60 & Younger 12khz 50 & Younger 14khz 49 & Younger 15khz 39 & Younger 16khz 30 & Younger 17khz 24 & Younger 17.4khz 24 & Younger 18khz 24 & Younger 19khz 24 & Younger 20khz 18 & Younger 21khz 18 & Younger 22khz 18 & Younger window.google_render_ad();

Interesting. Even the listening equipments - computer speakers,phones,Hi-fis have a best processing range. This is by design is supposed to correspond the best hearing range of humans. Most of home systems have upto i.e 18 KHZ or thereabout. It could somewhat explain why u are not able to hear some high pitch sounds,because the sound systems perform poorly,although aging is another bigger factor. For those who can hear very high pitched sound with this systems,it means their sensitivity is high. Compare this with mosquitos or bats or other small animals,their sensitivity is super super. If you can acheive enough power for the sound - you can chase them - that is before they get conditioned.