New Pet Training Dog Adjustable UltraSonic Sound Whistle Dog whistle with the dog (can also be used for other pet birds such as pigeons) While using this product can produce ultrasound and spread very far.Within 3km can be heard. This is Pet Training Dog Adjustable UltraSonic Sound Whistle. This Whistle can help you to train your dogs. Note: Dog whistle is about 5.2 CM long, the band length is about 6.5 CM The sound can be heard by human as well . please don\`t worry! Dog whistle will send a dog can detect ultrasound. to establish a good tool for communication and discipline. Ear of dog to receive sound waves per second, 120 kHz, while the people can hear up to 20 kHz. Dog whistle can be issued in addition to the human voice can be heard outside the tube, while the sound people hear is, only dogs can hear frequencies, this frequency ultrasound transmission is very far, so the dog can be very far away hear the sound.