Not too long ago we heard about Google rolling out the “Hey Google” hotword to Android devices to make Google Assistant a little more conversational. It isn’t fully replacing “Okay, Google,” but is instead being offered as an option, and that change is starting to roll out to some devices right now.
This command only worked on Google Home devices before now, so it was a long time coming. And, like Google Home devices, you can still use both commands on your phone, so you don’t have to pick and choose.
If you haven’t already seen the notification on your phone, hit up the Play Store to see if you’ve got a pending update for the Google Search app waiting. Once that update hits, you’ll be good to go.
source: Droid Life