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. Point unit directly at the dog and press the button for a few seconds.The ultrasonic sound should discourage the dog from approaching. Press button for a loger period of time if necessary. Please note that the prime operating range is 5-6 feet but it should be effective up to 20 feet. Important Tips: Dog Repeller will get an immediate response from most dogs. Others may require repeated enforcement. Never go near an animal that seems dangerous. Dog Repeller will discourage most dogs but may not be effective in all situations. Use good judgement when approaching animals taking care not to surprise them.