Google's new app Duo is a simple video calling service that's now available for android and iOS.
In a way, it's the company's answer to Apple's Facetime.
And it works very similarly.
So here's what you need to know about Duo.
First, there's Knock Knock which gives you a preview of who is calling by firing up the camera on the other end of the line.
If you're initiating the call, you'll see a little notice that says your video is visible.
Android users can see Knock Knock regardless of whether Duo is opened or not.
In IOS though, you'll only see it if you're in the app.
Otherwise, you'll just get a notification saying someone's calling you.
Now, before you worry about seeing anything you don't wanna see from the other line, know that you can only receive Knock Knocks from people who are in your contact list.
You can also block individual people from calling you.
And if Knock Knock really isn't your thing you can disable it all-together.
At this point you might be wondering what makes it different from Google's other communication platform, Hangout.
Well, according to Google, Duo is supposed to be way for specialized.
Whereas Hangouts is cross platform and supports group chats and multi-way video and messaging, Duo does one thing, and one thing only, video calls.
Unlike Hangouts, it reaches people through their phone numbers, not their email.
And the best difference between it and Hangouts?
It uses end-to-end encryption.
Because Duo is more streamlined, it has a very minimalistic user interface.
Before you start a call, you'll see icons to start a video call, and your contacts.
during a call, you'll see yourself, and icons to mute audio, switch cameras, and end the call.
Video from the other line fills up your screen, and that's pretty much it.
For more about Google's Duo app, check out our hands-on at cnet.com.