This was an option on the Moto X second generation phone. I have no clue why Google decided to remove the feature of setting the wakeup phrase, but at the time they were actually touting it as an upcoming feature (I guess to get me to upgrade my phone).

So being forced to say ”OK Google" is actually a regression from previous capability.

https://www.droid-life.com/2014/12/04/moto-x-tip-use-a-whist...