[Automatic Dog Bark Control] The device detects dog barking up to 15 meters away and automatically emits an ultrasonic sound to distract your dog and stop unwanted barking. So you can enjoy a moment of peace. [Dog Bark Control] Ultrasonic frequencies are harmless to pets and completely inaudible to the human ear. If your 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 Working Levels] The dog bark control device with adjustable frequencies is suitable for different dogs. 15 kHz - 30 kHz is suitable for large and medium-sized dogs. 20 kHz is suitable for docile dogs. 30 kHz is suitable for small dogs. It is recommended for dogs aged 6 months to 8 years. [USB Rechargeable] The ultrasonic dog repeller has a built-in rechargeable lithium battery and can operate continuously for 30 days after a full 5-hour charge. The red/blue color indicates the battery status. [Easy