STI Rex Plus II Electronic Watchdog Alarm. Rex II, the electronic watchdog alarm never needs sleep, a walk, food or water, yet is always on duty guarding and protecting. When Rex II detects movement, he starts to emit the user selected sound (i.e. barking dog). The closer the intruder gets, the more frequent the barking becomes. As the intruder backs off, the barking decreases in frequency, stopping completely when movement is out of range. In addition to the choice of a ferocious dog or dogs, Rex II also offers a siren or greeting announcer. Rex II is versatile and provides an excellent way to deter burglars, without the annoying problems of owning a real dog. With his electronic radar eyes, Rex II can "see" through thick doors, walls and glass. Once his cord is plugged into any standard 110 VAC electrical outlet (or install six C batteries), he"ll stay on duty around the clock.