If you use "OK Google" to invoke the Assistant on your phone, things are about to change. Google is removing the "Unlock with Voice Match" feature, so the Assistant is going to get a lot more secure.
Currently, if you use the "Unlock with Voice Match" feature, you can completely unlock your phone with Google Assistant just by saying "OK Google." While convenient, this is also a pretty big security risk---your voice isn't exactly the best way to verify that you are, well, you. If someone else's voice is similar enough to your own, then they can easily use this to unlock your phone and gain full access to it.
But now, Google is removing that feature from all Android phones. It started with the Pixel 3 and 3 XL, but confirmed that this would also get canned on all other Android devices in the future---a future that has apparently arrived. The Moto X and Pixel XL are the first devices to lose this functionality, so it shouldn't be too much longer before it's removed on others, too.
Of course, with this increase in security, you'll also get a loss in functionality. Anything that would require you to unlock your phone---like sending a text message, for example---will no longer be an option. It's sort of a bummer, no doubt, but it's a tradeoff that's worthwhile.
Without the Voice Unlock feature, Assistant will be limited to "personal results" only. According to 9to5Google, This includes:
- Email, including personal results from Gmail, like flight reservations and bills
- Google Calendar
- Contacts
- Reminders
- Memory aids
- Shopping lists
Anything more will require the phone to be unlocked before proceeding. Similarly, you'll no longer be able to tap the home button to go directly home after calling up the Assistant---you'll have to unlock the phone with your PIN, pattern, passwords, or biometric verification first.
9to5Google via Engadget