The PetSafe PBC00-11216 Outdoor Bark Control Birdhouse is a great approach to solving a dog's outdoor barking behavior.  The birdhouse unit has an internal microphone that detects barking, activating the unit.  This barking deterrent is effective for barking dogs up to 50 feet.  When activated by barking, the birdhouse will emit an ultrasonic sound that can only be heard by dogs.  This pitch startles the dog and distracts them from barking.  The unit has 4 settings that include 3 Sensitivity Levels and a Test Mode. 

The birdhouse can be hung from a tree branch, blending in nicely with your yard or simply placed in the target area.  Try to place in an area that is free from large objects that would be an obstruction between the dogs area and the unit.

Note:  The PBC00-11216 Outdoor Birdhouse is designed for outdoor use only, for a ultrasonic bark deterrent used indoors, please see the PBC-1000.