Google Duo: New video chat app that lets you see people before they ring you launched

The app's biggest distinguishing feature – and its most controversial – is that you can see people while they wait to talk to you

Knock knock. Who’s there? Google’s confusing chat app.

The search giant has released a new video call service called Duo that will take on other apps like FaceTime, Skype and Facebook Messenger. Google hopes that it can beat out those other services with two main things: being available on every platform and offering a special feature called “Knock, knock”.

That tool means that when someone is ringing, they come up on the screen before the call is answered. That lets the person being called see who’s ringing them – but it doesn’t show anything from the camera until the user actually answers the call.

Some have argued that feature could prove controversial, forcing people to see inappropriate pictures, but it can be turned off.

It was shown off earlier this year as part of a range of new tools – and is finally making its way to both Android and iOS.

Like with FaceTime – but unlike almost every other competitor – Duo only needs a phone number to talk to someone. Most other services, including similar ones made by Google, require that both people sign up and register new usernames.

Google has long offered video calling, through its Hangouts and chat apps. But it is moving Hangouts into a business-focused app, and hopes to make Duo the new way that Google users will call each other.

As such, it is intended to be more simple and reliable. It will also make sure that it works well on slower connections, by using Google technology to compress video streams.

Google has another mobile messaging app on the way this summer. The second will be called Allo, and is a more traditional chat app that integrates Google’s artificial intelligence to help people consult a robot during their conversations.