When using “Audio” mode, you will hear the device activate. It's recommended you use this mode when adjusting the bark sensitivity when first setting up the unit. In addition, you can use the audio mode for older dogs or dogs with poor hearing as an alternative to the ultrasonic sound training. Using the Audio mode when setting up the device will be key into accurately gauging the sensitivity of the microphone. You will be able to hear if the device is activating too often or not often enough. Adjust the dial up or down as needed and once you hear the unit ONLY activating when the dog is barking then you can flip the switch to the Ultrasonic mode.