When your dog barks, the Bark Control Collar gives a warning beep and mild correction. Then if he continues to bark, he will receive the warning tone with a slightly stronger correction. The process will continue up through six levels of correction. The collar senses the vibrations in your dog's throat that happens only during barking. While not at all harmful, The Bark Control Collar is an effective deterrent to excessive barking. For dogs over 8 pounds.