A dog whistle (also known as silent whistle or Galton's whistle) is a type of whistle that emits sound in the ultrasonic range, which people cannot hear but dogs and cats can. It is used in the training of dogs and cats. It was invented in 1876 by Francis Galton; the whistle was mentioned in his book Inquiries into Human Faculty and its Development. In his discussion (Galton 1883:26-27) of his experiments to test the range of frequencies that could be heard by various animals, he notes that cats have the most all-round sensitive hearing, being able from a considerable distance to hear notes too high in frequency for humans to hear, and small dogs can also hear these notes, while large dogs cannot.
The range of human hearing is typically considered to be between 20 Hz and 18 kHz. The top end of a dog's hearing range is about 45 kHz, while a cat's is 64 kHz. It is thought that the wild ancestors of cats and dogs evolved this hearing range in order to hear high frequency sounds made by their preferred prey, small rodents. The frequency of most dog whistles is within the range of 23 to 54 kHz, so they are above the range of human hearing, although some are adjustable down into the human range. To human ears, a dog whistle makes a quiet hissing sound. Some dog whistles have adjustable sliders for active control of the frequency produced. Trainers may use the whistle to simply gather a dog's attention, or to inflict pain for the purpose of behavior modification.
In addition to lung-powered whistles, the term dog whistle is also used for electronic dog training devices that emit ultrasonic sound via piezoelectric emitters. The electronic variety are sometimes coupled with bark detection circuits in an effort to curb barking behavior.
These kind of whistles are also used to determine the hearing range of people or for physics demonstrations.