http://www.techradar.com/news/google-home-mini-bug-caused-devices-to-record-247

When putting an internet-connected device with a microphone in it in your home there's always the risk that it could be constantly recording and sending your data to its manufacturer. 

For some owners of review samples of the Google Home Mini, this worst case scenario came to pass as their devices were found to be constantly recording and sending the audio data to Google.