Unleashed Technology has a really new and unique training system based on the science of how dogs learn. Using a combination of the exclusive adjustable vibration and stimulation method, your dog will quickly learn obedience, sporting or competitive commands. All Unleashed Wireless Leashes feature: a unique transmitter for left or right male or female hands; 1,2, 3 button models available, GT-1, GT-2, GT-3, an exclusive adjustable vibration, Unleashed amplified cell phone vibration so dogs respond, and a special automatic alerting system, all dogs deserve the respect to alert them what is required before vibration or stimulation continues. The add-a-2nd Dog Option allows you add another collar to your existing model. Rechargeable and replaceable NiMH batteries.