A new, smaller and more compact waterproof collar makes this unit lightweight and comfortable. It fits small to XXL-sized dogs, and sports a built-in magnetic, on/off system. These collars operate on an NiMH, 4.8 rechageable battery system that can deliver 1/2-second corrective stimulation. The redesigned digital system has a micro-processor and a vibration sensor that only picks up a dog's vocal cord vibrations, preventing the collar from responding to outside noises or clinking from your dog's tags. The digital numeric display shows the eight different intensity levels, and the data memory system saves the last intensity setting you used. Each also has an automatic three-second safety delay. Size: 2-1/2" x 1-5/8" x 1". Weight: 4 oz.