Super bark free has a specially designed sound selector that lets you choose the ultrasonic frequencies which can only be heard by dogs and cats, or lower sound tones audible to human ears. Super bark free uses an age old principle of "Negative Reinforcement using sound" to help train dogs to stop annoyance barking. The attachable target dome increases the operational range to 50 ft, twice that of the original bark free. Powered by 4 "D" batteries, this allows the bark free to operate anywhere in your yard, and not just near an AC outlet. The adjustable bark selector allows you to program exactly how many barks will activate the system, with either 1, 2, 3, or 4 barks to choose from.