Ineffective against dogs in the following situations: 1. Your own dog, because it knows it won't be harmed by its owner. 2. Noisy environments such as downtown areas or roadsides. 3. Dogs with their owners - dog fights. Well-trained large dogs - they are well-trained. 4. When the battery voltage is too low - the transmission power will be low. Features 1. The bark control device is a safe and effective training tool, and the dog bark control device is very safe for dogs, using normal sounds and ultrasonic dog whistles, which are harmless to dogs. 2. This bark prevention device can quickly train dogs outdoors or indoors, change pets' bad habits of barking, and guide dogs' savage behavior. 3. A dog device to stop barking, suitable for dogs of all sizes. Bark Prevention Device - Lighting When you slide the dog bark prevention function switch to the "Lighting" position, it can be used as a flashlight, making it easier to walk your dog at night and illuminating the way back. Bark Prevention Device - Dog Training Slide the dog bark prevention function to the "Train" site. The bark prevention device emits low-intensity ultrasonic waves, helping to correct excessive barking, fighting, and bad behavior. Bark Prevention Device - Chasing Dogs Slide the dog bark prevention function switch to the "Chaser" site. Facing the dog for a few minutes, the flashlight of the bark prevention device will flash, and high-intensity ultrasonic waves will be emitted, helping to drive away other dogs. Notes 1. These bark control devices are not recommended for dogs under 6 months old or over 8 years old. 2. This bark control device is ineffective for dogs with hearing problems. 3. Effective for timid dogs, especially stray dogs. It may not be effective if your dog has enough trust in its owner. We recommend purchasing according to the actual situation. If you purchase the "Dog Repellent", batteries are not included. This product supports 9V (006p) dry cell batteries! Please understand that the package has some damage. Shipping will be via Yu-Packet Post.