"Hey Google" hotword is rolling out to Google Assistant on phones
A growing number of users are receiving a prompt to setup voice recognition within Google Assistant again with the new command. All you need to do is repeat the phrase a couple of times as needed, and you're all set. Optionally, you can also ignore the prompt and keep on using the "Ok Google" hotword.
To manually check for the option, make sure that Google Assitant/Search are up to date and go to Settings > Google > Search > Voice > Voice Match to see if the "Hey Google" command has appeared.
That's cool and all, but we can't help but wonder, when is Google simply going to allow us to set our own custom hotwords?
source: AndroidPolice
Things that are NOT allowed: