PetSafe, In Ground Electric Stubborn Dog Fence With Collar, For Pets 8 LB & Up, Comes With 500' Of Wire, Surge Protector & Flags, Can Expand Up To 25 Acres With Additional Wire, 4 Levels Of Static Correction With Highest Intensity Available For The Most Stubborn Pets, Vibration & Tone Options Included, Anti Linger Prevention, Progressive Run Through Prevention, Low Battery Indicator, Expand to Unlimited Number of Pets With Additional Collar #PRF-275-19, Uses 9V Battery, Not Included.