Google has made a very new and significant change to its Duo app. With the update, Google Duo users can now 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. Recipients can answer the call by dragging up on the phone icon, mute their mic or change cameras, and hang up just like a regular Duo call. It was first spotted by a Reddit user.>
And in case a user hits a button to navigate away while the Duo call is connected, similar to how a full-fledged app functionality would allow you, it will show you a persistent notification icon that can bring the call back into view, at any point.
At the end of the call, these users will be prompted to install the Duo app; that will remain a choice. Additionally, these users will also get a notification, which will allow them to block a caller from contacting them, or if you choose to continue receiving calls.
You must definitely be wondering, how does Google make this happen? Well, this is done via a feature of Google Play services called App Preview Messaging, which launched alongside Allo back in 2016.
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.
Source : http://www.bgr.in/news/google-duo-now-lets-you-call-people-who-dont-even-have-the-app-installed/402