Protect yourself from dangerous dogs while cycling, walking, or jogging with the Ultrasonic Dog Repeller. It produces a high frequency sound that the human ear can not detect, yet it is able to deter vicious dogs without harming them. It's even safe enough to use for training dogs. To repel dogs, point unit directly at the dog and press the button for a few seconds. The ultrasonic sound should discourage the dog from approaching. Press the button for a longer period if necessary. Prime operating range is 5 to 6 feet, effective up to approximately 20 feet. Features a low battery indicator. Note: Do not use on human or within one foot range of a pet. Requires one 9 volt Alkaline battery.