You probably can't hear a dog whistle because the frequency is too high. Dogs hear higher frequencies better than people do. That’s why dog whistles seem to be silent. High frequency sounds usual travel further than voices.
Dog trainers use dog whistles to get a dog’s attention. Some think different breeds react to different high frequencies. Smaller dogs are more sensitive to higher frequencies.
Dog Whistle Downloads
These dog whistle MP3 files can be used to train your pet. Download them and make dog whistle ringtones for your cell phone. Or use them as the startup sound or mail notification sound in your computer to fool your pet. (Think prank!)