Last month, Google's sister company Nest revealed a smart doorbell, the Nest Hello. It has a built-in camera with IR illumination, and is able to detect faces with Nest Cam IQ. Google is leveraging that feature with a new voice command for the Google Assistant.
At today's press event, the company announced that Assistant will automatically broadcast to your Google Homes the name of the person that rings the Nest Hello doorbell if it recognizes the face. Pretty awesome. It wasn't explicitly confirmed, but this feature will likely go live once the Nest Hello goes on sale in 2018. Of course, if Hello didn't recognize the person, or if you want to see what's going on outside, you can ask Assistant to stream the video feed to a nearby TV.