Sound Barrier 3-Station Indoor Sonic Dog & Cat Fence SB-3 Indoor electronic pet barrier for dogs and cats uses audible sound, not shock, to keep your pet out of restricted areas The lightweight electronic collar sends an ultrasonic signal that triggers a loud sonic blast at the receiver unit to make your pet scat Alarm is triggered only by your pet's individual electronic transmitting collar, allowing people to come and go without triggering the alarm Pet collar weighs only 1 ounce and is suitable for large dogs or small kittens Includes 3 receiver modules and one pet collar; collar comes with lithium battery, standard 9-volt battery required for each receiver (not included)