How this bark control collar works?An internal microphone picks up the sound and the unit is automatically activated. The bark control collar starts with emitting an ultrasonic sound of 1 second as a warning at the first bark. At the second bark the collar emits an ultrasonic sound of 2 second. From the third bark the collar emits a 3 second ultrasonic sound and gives 2-3 seconds static shock. The dog should stop barking. If the dog barks within 1 minute after the first static shock, the collar sends out a 3 second ultrasonic sound and 2-3 second of static shock. If the dog stops barking, the collar resets itself to the lowest level and repeats the first 3 steps. The shock levels can be adjusted with the delivered screwdriver. If you find the light is on but the collar doesn"t seem work, please try the following steps: 1 Make sure that the metal probes contacting with your dogs neck snugly,more specific,the metal probes must contact with your dogs vocal cord to capture vibration while it is barking. Because the collar won"t be triggerred off by ONLY sound. The collar will only be activated with both bark and vibration of your dogs throat being detected. The unique design of this collar will keep your dog from hurting by any noise. 2 If you dog ignores the current vibration/shock the collar emitted, then please change the sensitivity of this collar. Follow the instruction in the last two pictures.Note: the more slim the arrow goes the more sensitive the collar does. 3 If it still doesn"t work, please contact our customer service for help. Package includes: Bark controller X1Adjustable Nylon Collar X1Standard AAA/1.5V X2Contact points X2 Battery capacity tester X1 Special screwdriver X1 Please note that this collar is only suitable for big dogs(60lbs--120lbs) not for small ones.