Safe anti-barking device for dogs: the ultrasonic dog trainer uses the principle of ultrasonic wave to stimulate the dog, whereupon the dog stops its current behaviour. When the device is turned on, it emits a frequency of 10 kHz to 30 kHz, which is difficult for human hearing, but a sensitive frequency for dogs. However, the sound does not have a negative effect on the hearing or health of dogs. Effective for dogs of all sizes: the ultrasonic anti-barking device for dogs has 3 adjustable frequency levels and is recommended for dogs aged 6 months to 8 years (15-30 kHz, suitable for large and playful dogs; 20 kHz, suitable for docile dogs; 30 kHz, suitable for small dogs). It can easily cope with various barking dogs. Adjust the frequency weekly to maintain training results. Three adjustable modes: the ultrasonic switch emits ultrasound to deter or train dogs. Flash light switches are used to amuse dogs. The LED light switch can work with the ultrasonic wave to stop the dog's barking. Some dogs are afraid of ultrasound or do not like it and may not stop barking at first. Please allow up to 2 weeks for training. Portable design: our anti-barking ultrasonic device is compact and portable. It is easy to carry when you walk your dog, walk or run. The effective range is 25 feet, perfect for training dogs at home or outdoors. It can also prevent other dogs from approaching you when jogging, walking or running.