An invisible fence is a type of pet containment system that uses a buried wire to create a boundary for pets, typically dogs. When a pet approaches the boundary, a collar worn by the pet emits a warning sound, followed by a mild static correction if the pet continues to move closer. This helps train the pet to understand the limits of their safe area. Invisible fences are often used as an alternative to traditional fences, providing a flexible solution for pet owners. They can be adjusted for different yard sizes and can accommodate various types of pets, making them a popular choice for many households.