Age Test is a fun gadget to find if you can hear different frequency of sounds. This sound is so called "Mosquito Sound", which gives off high-frequency noise. Test it with your friends and family!

From wikipedia:
Hearing range usually describes the range of frequencies that can be heard by an animal or human, though it can also refer to the range of levels. In humans the maximum range of audible frequencies normally lies between 16 Hz and 16,384 Hz (16.384 kHz); not to be confused with the common sound system speaker range of 20 Hz to 20 kHz (Hz is the standardised term for 'cycles per second'), although there is considerable variation between individuals, especially at the high frequency end, where a gradual decline with age is considered normal.