Automatic Dog Bark Control The device intelligently captures barking dogs from up to 15 meters away, and automatically emits ultrasonic sound that distracts your dog to stop unwanted barking, so you can enjoy 'a moment of peace and silence. Dog Bark Stopper Ultrasonic frequencies are harmless to pets and completely inaudible to the human ear. If the dog is hard of hearing or aggressive, the device may not work as expected. It is not recommended to use one device against two or more dogs barking at the same time. 3 Levels of Operation Adjustable frequency dog bark deterrent is suitable for different dogs. 15KHZ-30KHZ is suitable for big bad dogs. 20KHZ Suitable for gentle dogs. 30KHZ Suitable for small dogs. It is recommended for dogs aged 6 months to 8 years. Rechargeable by USB Ultrasonic dog repellent incorporates a rechargeable lithium battery, the device can work continuously for 30 days after have been fully charged within 5 hours. Red or blue color indicates battery status. Easy and Waterproof Installation Dog bark stop device can be hung on tree, wall or fence to prevent your own dog or your neighbors' barking. Make sure the bark controller is facing the dog within reach without any obstruction.