Find the highest frequency you can hear. Slide up slowly until the tone disappears. A rough, fun check of your high-frequency hearing, not a medical test.
Typical limits: most adults hear up to about 15–17 kHz; this drops with age (often ~17 kHz at 20, ~14 kHz at 40, ~12 kHz at 50+). Mosquito-tone territory is 17 kHz and up. This is a rough self-check, not a hearing assessment, and depends heavily on your speakers and volume.
Set a comfortable volume, start the tone at a low frequency, then slowly slide it up. The highest frequency you can still hear is roughly your upper limit. Slide back down to confirm where it reappears.
Healthy young ears hear roughly 20 Hz to 20 kHz. The top end falls with age and noise exposure, so many adults top out around 15 to 17 kHz, and tones above 17 kHz (the so-called mosquito tone) are often inaudible to older listeners.
No. It is a rough, fun self-check that depends entirely on your speakers or headphones and volume, which cannot reproduce all frequencies evenly. For any real concern about your hearing, see an audiologist.