The Nest Hello's microphone can pick up sound from all directions, which can be both a blessing and a curse. The 3-microphone array within your Nest offers automatic adjustment of sensitivity, to smartly pick up on just the sounds you need. What this does mean, though, is that you cannot manually adjust the microphone sensitivity up or down - you are at the mercy of Google's algorithms to get it right. You can, however, turn off the microphone completely under Settings -> Microphone -> Audio recording, or enable a temporary Quiet Time from the home screen of the Nest app.