ULTRASONIC TRANSMISSION:This professional dog whistle emits ultrasonic waves that are not easy to detect by human ears but dogs can hear very clearly. Therefore, even if the dog is far away, it can be recalled without worrying about too much noise. . ADJUSTABLE FREQUENCY:The frequency of the ultrasonic dog whistle can be adjusted. At first,you can loosen the sound wave adjustment screw, then while blowing into the air inlet, adjust the adjustment lever to the appropriate volume, and finally tighten the sound wave adjustment screw. . PURPOSE:Pet whistle is very suitable for domestic dog, guide dog and rescue dog training. You can train the dog by setting the whistle commands. For example, two long tones are to recall, two short tones are to stop barking, and one short tone is to sit down , so as to regulate the dog's behavior and make the dog get along with people more harmonious. . EASY TO CARRY:Each ultrasonic dog training whistle is equipped with a black rope, which is convenient to carry with you. It can be hung around your neck, which reduces the risk of losing the whistle and is also easy to use. . PACKAGE CONTENT:Buy this product, you will get 4 different colors of ultrasonic dog whistle, which are black, red, purple, orange, multiple colors, each family member can use one. .