Finally, the first Dogtra expandable system is available. Dogtra EDGE is a fully customizable and expandable e-collar (up to 4 dogs) designed for professional and serious amateurs. The New Dogtra EDGE RT, on the other hand, is designed for the most demanding training environments. Whether you're a professional trainer or a serious amateur, the RT offers the simplest solution to the most complex training. The RT transmitter gives you a 'no look' one-hand operation, so your eyes are always focused on your dog.