Small and lightweight, the eXtreme Dog Fence? Add-On / Replacement Dog Collar accommodates dogs from 8-120 pounds. The receiver collar?s small and slender profile is more ergonomic than other collars on the market. It has 8 levels of correction to choose from, which are as follows. Setting 0 on your transmitter is a tone-only mode, used for training. Levels 1-5 are low to high correction levels. Levels 6 and 7 are progressive correction. This means that the collar senses how quickly your dog is moving toward the wire, and ramps up the correction level accordingly. Each collar can be individually set to ensure you can tailor the correction level specifically for each dog. The collar is powered by a lightweight 6 volt Perimeter battery that typically lasts between 3-4 months. To replace it, you just unscrew the compartment on the collar.