Dog whistle will send a dog can detect ultrasound. Ear of dog to receive sound waves per second, 120 kHz, while the people can hear up to 20 kHz. This Whistle can help you to train your dogs.Using this product can produce ultrasound and spread very far. Within 3km can be heard. 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.