Containment Systems Give Dogs the Freedom to Run Within the Safety Of Your Yard Features: Rechargeable collar receiver Up to 25 acre coverage Battery back-up Run-through prevention Creating an in-ground, hidden fence is easy with Smart Dog Containment Systems. The collar receiver will deliver a warning tone as the dog approaches the boundary and correct the animal with a harmless but effective static correction if it continues toward the boundary. Dogs learn to obey warning tone to avoid the static correction. System can also be used to block off areas of the yard where dogs are not allowed. Collar is equipped with Innotek's smallest rechargeable, waterproof collar receiver, which delivers stimulus in three levels of stimulation. Unique run-through protection feature boosts stimulation to high level if dog does not return after initial stimulus. Also features built-in lightning protection, additional external lightning protection, a wire break alarm, and omni-directional signal. Battery back-up feature (8 "AA" batteries not included) powers system up to 40 hours and has an alert feature to signal that batteries are being used. Add Boundary Kits to increase basic 500' perimeter coverage to 25 acres. Each kit (see item ZX936 sold separately) increases coverage by approximately 1/2 acre. Additional collar receivers are also available and sold separately for multiple dog households. For use with dogs over 5 lbs and at least 6 months old. Collar fits necks 9 1/2"-23". Smart Dog Premium Containment System includes wall-mount transmitter, AC adaptor, rechargeable collar receiver, 500 ft of 20 gauge boundary wire (to cover approximately 1/2 acre), 100' pre-twisted FasTrak wire, 50 training flags, two sets of collar probes, test light, and training video.