This is the only hidden cat fence that confines your feline to your yard without physical barriers that are often unsightly and ineffective. The underground electronic fence sends a warning tone to the included collar as the cat approaches the unseen barrier. If the feline crosses the boundary, the fence transmits a harmless, mild static energy pulse that prompts the pet to turn back. After just a few exposures, the cat will learn not to encroach on the restricted area. The boundary wire can be buried in a 1" to 3" deep trench or attached to an existing fence to secure the perimeter of a yard up to 1/3 acre. The boundary wire connects to a transmitter that mounts to a wall indoors and allows you to adjust the static energy pulse to four different strengths or emit only the warning tone. It comes with a DVD that guides you through installation (including how to cordon off trees or pools) and provides step-by-step instruction for training your cat. Includes 500' of boundary wire, 50 flags that serve as visual reminders of the underground fence, and a replaceable battery that lasts up to two months and is widely available at pet stores. The system is designed for cats weighing at least 6 lbs. and 6 months of age or older. Transmitter plugs into AC; 4 3/4" H x 4 1/4" W x 2" D. (8 oz.)