I bought the handheld Dazer II ultrasonic dog deterrant. I have 3 barking dogs at night that bark at possums, and even if they are not there they bark regardless. First night, they were barking their heads off, I pressed the buzzer for 1 to 2 seconds only. Immediately stopped. Never barked after that. So happy with this product. I rang my vet to ensure it was a safe product and he said it was fine. No more barking dogs to upset my neighbours.