Google is listening... as well as every company that may have some sort of a voice assistant. 
Like Google's Google Assistant where it needs to listen for those magical words - "OK Google" or recently added, "Hey Google." For the assistant to know you said these trigger words, the device needs to listen continuously via its microphone. Thus, it may hear "OK Google" and pretty much every other word you say whenever you're near your phone. 


More on this - http://www.news.com.au/technology/online/security/google-is-recording-everything-you-say-to-a-bot/news-story/fcf90d5c6b20acb9cf35d1e6c029a3ac