XDA contributors have found that Google has included code that supports its long-touted "Lift to Talk" setting for Assistant in its app. This feature allows the voice-activated AI in question to be prepared to answer queries whenever a user holds a given device up to their face. However, the researchers have found this option is still buggy when enabled.
https://www.notebookcheck.net/Google-s-Assistant-may-soon-add-the-Lift-to-Talk-feature.442652.0.html