My Nexus 5X on Google Fi asked me if I wanted to try out the Trusted Voice feature last week so I did. Unfortunately it makes the phone wake and show an invalid lock message when people around me or on TWiT shows say OK Google or sometimes just Google.
Then something happened that showed me how much this feature lowers the secutiy of your phone. I was watching All About Android and Aaron Newcomb said OK Google multiple times during his conversation with Ron Richards. My phone kept showing the bad unlock screen and going back to sleep until one time it unlocked! Oops, I decided that the convenience of this feature was far outweighed by the reduction in security so I turned it off.
Paul Hutchinson's Blog 