Here's why you might get Google Duo calls on your Android phone without the app

Google Duo is Android's official answer to FaceTime, allowing you to make simple and stable video calls to friends and family. Thanks to a new update just pushed out by Google, you'll be able to receive calls made by the Duo app on some Android phones, even if you don't actually have the app yourself.

Android Police spotted the update, which means audio and video calls will pop up on some Android phones even without the app – it's not clear exactly what the criteria for this is, but having your phone number registered with Google seems to be part of it.

It all happens through something called App Preview Messaging, which works through a background Android app called Google Play Services. The tech allows some basic bits of an app to essentially operate as part of Android, so you can get in touch with people no matter what messaging apps they've got installed.

Knock, knock, who's there?

Some of the best parts of Google Duo, including the "knock knock" feature that lets you see who's calling on screen before you answer, are included in this new functionality. At the end of a Duo call, users are asked if they want to install the app, if they don't already have it installed.

Obviously this won't work when making calls to iPhones, but it makes life a little easier for Google Duo users – you don't necessarily have to fret about whether your contacts have Duo installed before placing a call.

Google hasn't said anything officially about the update, but it continues to push Duo and the text-based Google Allo as its messaging apps of choice, even with the likes of Google Hangouts still loitering around in the background.