PetSafe Stay & Play Wireless Fence Extra Transmitter EXPAND YOUR BOUNDARY - increase your pet's play area with an extra transmitter. Transmitters boundaries need to overlap 30 ft. PORTABLE - no wire to bury ADJUSTABLE - circular boundary up to 3/4 acre EASY SET UP - in as little as 1-2 hours COLLAR SOLD SEPERATELY - Requires a PetSafe Wireless Fence Receiver Collar to operate Item does not work with mobile homes, structures with metal siding or structures with metal roofs Call, chat or email with our expert PetSafe US-based customer care specialists six days a week; They are waiting to assist you and your pet with your product needs