Just like it sounds, the feature essentially allows users to leave voicemail-style videos for any user who misses or declines a call on Duo. The messages can be 30 seconds in length, and they’ll also automatically disappear after a day, although recipients can download the videos to their camera rolls.
Google Duo has been making some very interesting additions to the app lately. Earlier this year, Google updated the app to allow users to call people that haven’t ever installed or registered with Duo in the past. It works almost exactly like a normal Duo call, including the Knock-Knock feature.
This means, for users who do not even have the app installed on their phones, an incoming call can instantly fly over the screen with a view of the caller’s camera. This also works with audio-only calls.
The ability to make Duo calls to people without it installed on their end should make it more accessible and reduce the complaints that “none of my friends use it”. However, this isn’t going to work with everybody on your contact list – iPhones and other non-Android devices are obviously off limits.