The Dogtra EDGE is a fully customizable and expandable e-collar designed for professionals and serious amateurs. Equipped with high intensity LED location lights on the receiver/collar, you are able to easily find and distinguish between dogs in low-light/dark conditions. Light options are white, red, blue and green. These "location light" colors correspond to the button colors on the handheld transmitter and can be set to light solidly or flashing. The EDGE comes complete as a 1-dog system, but is fully expandable to a 2-dog, 3-dog, or 4-dog system with the purchase of optional receivers (sold separately). With 1-mile range, and a fully waterproof receiver and transmitter, this system offers all of the features needed for any conditions. The 2-hour rapid charge Lithium Polymer batteries are housed in a separate compartment on the transmitter/receiver for easy replacement. The EDGE has the ability to switch between the rheostat intensity (for smooth gradual adjustments in intensity) to a selector/step dial with 8 "click-able" levels of stimulation. Nick, constant, and vibrating page options allow even more training flexibility. The standard 5/8" contact points can be extended to 3/4" for use with dogs with longer coats. The LCD Screen not only displays the exact level of stimulation, mode, and battery life, but is back-lit to match the color of the collar you are activating. A truly feature-rich system!