Hi. It sounds as though you might not have given MixEmergency permission to use the Microphone input of your computer. First, please make sure that you've copied MixEmergency into your Applications folder, and that this is where you're launching it from. Second, after launching MixEmergency, and getting this message that you can't use the audio device, go to your System Preferences, to the Security & Privacy settings, and then to the Privacy tab on this panel. Click "Microphone" in the list on the left side of this panel. Is MixEmergency listed here? And if so, is it enabled?