Yard Barrier 3-Station Outdoor Sonic Dog & Cat Fence  YBR-3 Uses sound, not shock, to keep pets out of flower beds and gardens, off porches, away from pools, ponds, trash cans or any other off-limits area Heavy duty waterproof outdoor receiver units (3 included) may be placed anywhere that's off-limits to pets Lightweight waterproof electronic collar sends an ultrasonic signal that triggers a loud audible sonic blast at the receiver when the pet approaches Allows people to come and go without triggering the alarm Requires three 9-volt alkaline batteries (not included)