SAFE FOR DOGS & HUMAN: The dog barking control devices will not disturb or harm people or dogs. It works by emitting a sound in a frequency band that only dogs can hear and humans cannot hear, to make the dog stop its annoying barking. So rest assured that barking deterrents are not harmful to human or dog hearing. AUTOMATIC BARK CONTROL DEVICE: Using the latest ultrasonic technology, the anti barking device only works when it senses a dog barking. It will automatically stop excessive, noisy dog barking and give you a quiet life! 4 LEVELS OF OPERATION: Four adjustable ultrasonic volume levels (Test, Low, Medium, High), provide a wide range of ultrasonic penetration: 12-50 FT. The ultrasonic dog barking control device effectively stop barking indoors and outdoors. You can turn the knob to test different frequency bands for best results. DESIGN & WATERPROOF: Our anti barking device is made of waterproof material, so it can be used even in rainy days. The bark control device can be easily hung from a tree, fence post or anywhere with the included lanyard, which can effectively stop any barking. Note: Do not submerge the bottom battery compartment in water. FITS FOR MOST DOGS: This anti barking device works for most dogs: 6 months to 8 years old (10-130 lbs), but does not work for dogs that are deaf or hearing impaired. If the dog does not stop barking when you first start using it, please allow 2 weeks for the dog to adjust.