The PetSafe Big Dog Rechargable Bark Control Collar has a unique patented sensor that provides the most reliable bark detection available. The Bark Control Collar uses both vibration and sound sensors to discriminate each bark from other external noises. An electrical stimulation is administered through the Contact Points on the collar only if both the vibration from the vocal chords and the sound from the bark match the same criteria. 10 levels of progressive static stimulation. Adjustable nylon collar for neck sizes up to 71cm.