Constraints in hearing high frequency sounds like Mosquito ringtones

The British inventor Howard Stapleton was the main person responsible for the development of the concept of the Mosquito ringtone which since its release in 2005 has been a rage and have been adopted widely in the United Kingdom.
About Mosquito ringtones
It is necessary to note that the concept of the Mosquito ringtone was developed in order to ward of teenagers from loitering around shops in the United Kingdom. The central idea was to ensure the development of a system which on the one hand ensured an end to the roaming of teens and at the same time it had to be a system which will not cause any form of distress or disturbance to the adult shoppers.
The result was the Mosquito ringtone and it was based on the principle of presbycusis. The presbycusis states that all individuals begin to suffer from hearing loss once they attain adulthood from about the age of 20 and as the age increases further, the condition worsens and while initially this is not evident, around the age of 45, it becomes quite clear.
Researches have suggested that beyond the age of 20, adults are unable to hear sound wave frequencies ranging above 18 KHz. However, since normal human interactions usually range between 200 hertz to 8000 hertz, this problem goes undetected in the initial years.
The Mosquito ringtone consisted of a frequency if about 17.4 KHz and therefore while it could be audible clearly to teens and youngsters, adults remained oblivious to its effects. There are various other factors as well which play a key role in affecting the inadequacy of hearing high frequency sounds.