The PetSafe Transmitter is a safe and effective way of containing your dog. This transmitter uses buried wires to emit a signal to your pet's receiver (not included), to deliver a mild shock if your dog goes beyond the boundaries of the fence. This correction is geared to get your pet's attention, but not harm him in any way. The PetSafe Transmitter will work with any Underground PetSafe Collar and can accommodate an unlimited amount of pets. Wires, flags and receivers required, but sold separately. Free Ground Shipping!