As Paul mentioned last week, “OK Google everywhere” has started rolling out to all Google Now users, and should be available to you right now. Unfortunately, as the gurus at Android Police point out, if you turn on your lock screen and enable “OK Google” on your lock screen, your phone isn’t as secure as it was before.
That’s because anyone can place a phone call from the lock screen without unlocking your phone by saying “OK Google” and telling it to call someone. You can also start navigating from the lock screen, too.
To be fair, this is probably functioning exactly the way Google intends it to. The whole point of this feature is to minimize your physical interaction with the phone and allow you to accomplish various tasks without having to touch the screen. Requiring a PIN, pattern, or password input would kind of defeat the purpose here.
Still, it’s not so clear in the initial “OK Google everywhere” set up that this is the intended behavior of this feature – so enable it with caution.[Android Police]