OSIR Outdoor Ultrasonic Bark Control for dogs with birdhouse theme [Battery Operated] PORTABLE: small and light,you can hang it on the tree or anywhere in outdoor. EFFECTIVE: With a Sound Activated Speaker to produce the ultrasonic + an Microphone,it can detect all dog's bark within 50 feet (please note this product may not work on deaf or hearing impaired dogs) SAFE: human can't hear the ultrasonic sound and it will associate the bark with unpleasant noise,when the dog stops barking the ultrasonic also stops NOTE:There is no need to turn on the bark controller whole day,it will run out your battery very fast. ATTENTION:The bark controller is not very suitable for the special dogs which the ears been covered,besides,not to use the device for a long time,it will Reduce the effect.