nyone in your home can interact with Google Home by saying the hotword, "Ok, Google".

All interactions with people who Google Home does not recognize are visible on the set-up account’s My Activity page

When someone other than the person who set up a Google Home interacts with the device and the device does not recognize their voice, their communication history is stored in the activity history of the Google Account used to set up the device, which can be accessed at myactivity.google.com. If you allow guests to use your Google Home, be sure they understand that those interactions will be stored by Google and that you can view and delete that information. When you have guests in your home, you can consider using the microphone mute button or putting the device away as well. 

Others in your home can add their accounts to your Google Home using Google Home’s multi-user functionality.  If they do this and Google Home recognizes their voice when they interact with Google Home, their interactions will be stored in their own communication history at myactivity.google.com.

Anyone can ask Google Home about private information you’ve allowed Google Home to access

If you do not set up multi-user functionality on your device so that your Google Home can recognize your voice, anyone in your home can ask about information you have made available to Google Home. Additionally, if Google Home’s multi-user functionality mistakes a recording of your voice or someone else's voice as you, Google Home may convey your information to that user. To prevent others from accessing private information like reminders and calendar entries from your Google Home, you can turn off Personal results in the Google Home app. This can be set device-by-device, so you can give a Google Home in your bedroom different access to your information than a Google Home in your kitchen.