PetSafe In-Ground Stubborn Dog Fence Kit With Collar for pets weighing 8 pounds and more. System includes 500 feet of wire to fence in about a 1/3-acre yard, a surge protector, and flags, allowing you to create a custom-shaped fence for your yard. It can be expanded up to 25 acres with additional wire. The receiver collar features 4 levels of static correction, with the highest intensity available for the most stubborn of pets. Vibration and tone options are also included for training purposes. Anti-linger prevention and progressive run-through prevention ensure your pet stays within the designated area. The low battery indicator alerts you when it's time to replace the 9V battery (not included). With additional collars (PRF-275-19), you can expand the system to accommodate multiple pets.