Add an unlimited number of collars to your Humane Contain electronic fence system. Our new RC-7 collar is compatible with all Humane Contain electronic fences made by High Tech Pet Products. It also works with the Radio Mat transmitter pad. Miniature electronics weigh only 1.3-ounce. Features the proprietary Pulsed Proportional Stimulus System found only on Humane Contain brand products. High Tech Pet's advanced dog training technology is based largely upon the use of Pavlovian auditory stimulus (training tones) to reinforce the main shock stimulus. All other dog fence brands use a tone speaker that is completely enclosed in the casing to avoid failure if the speaker gets wet. This type of device doesn't make much sound and does little to aid in boundary training. The advanced RC-7 collar uses a special, waterproof speaker that transmits sound directly to the air for a much louder and more effective audible training stimulus. Then we pulse the training tones to follow the shock pulse rate. This yields a powerful enhancement to the training process, resulting in quicker, easier training and a more humane experience for your dog. Add to all that a beautiful, yet nearly indestructible, poly-elastomeric strap that is integral with the electronics casing, and you've got a state-of-the-art electronic collar at an amazing value. The strap is adjustable from 7 to 25-inch for all dogs 5-pound and up.