Dr.Tiger 2 Receivers Electric Dog Fence, Invisible Fence for Dogs, Collar Send Beeps and Shock Correction, Black-3 The electric 2 dog fence system is good to train dogs to stay within designated areas or away from roads, flower beds, swimming pool and other potentially hazardous zones. Static correction is automatically adjusted based on how close the dog is to the boundary, create a customized safe containment for pets to play outdoors. If you dont want shocks to dogs, plastic probes are available in the package. Thicker gauge wire can provide more stable harmless radio signal. Boundary wire is 650 feet long and 40 boundary flags.To avoid unwanted high voltage from lightning which may burn the transmitter, please consider buying a surge protector for the system from:https://www.amazon.com/dp/B000P7NX9S. 2 rechargeable and rainproof receiver collars.Please search https://www.amazon.com/dp/B073GXPP2R for extra receiver. Suitable for dogs over 8 pounds. Please test the collar in your yard to see whether it is activated by other same signal band frequency before insatallation. Return it when this appears. Our policy: 30 days money back or replacement for no reason. Any question, please just contact us. Our professional service team will always reply you as soon as possible. Dr. Tiger brand support phone: 9292731080( available from 6pm to 2am, from Sunday to Thursday, at American PST).