Outdoor Bark Control Disguised as a birdhouse, the unit emits an ultrasonic tone when your dog barks that can be annoying to your dog but is silent to most humansSmall Outdoor Spaces Each weatherproof unit covers just over 1,000 square metres; add more units to cover a larger space; hang them in a tree or place on a solid surface outsideGentle Bark Control The high-frequency tone (which humans cant hear) works on dogs of all sizes from 6 monthsBuilt-in digital alarm The timer works like an alarm clock, turning the unit on and off at specific times to stop your puppy from becoming desensitised to the ultrasonic tone