Google is going after FaceTime and WhatsApp and other video-calling apps with its own solution called Duo.

Duo is free to use and enables 1-to-1 video calls. It relies on your number, lets you reach people in your phone’s contacts list, offers end-to-end encryption, and has nifty features like Knock Knock, which lets you see live video of your caller before you answer. And it's super easy to use, because the app's interface is ridiculously simple. Here's how Duo works, including details about how to get started and whether its safe to use.

Google unveiled Duo at its Google I/O developer conference in May 2016. It has described Duo, which is free and available for iOS and Android devices in the US as of 16 August 2016, as a "simple video calling" app for everyone. It's basically a FaceTime/WhatsApp/Skype competitor.

Getting started

First, download the app for your iOS or Android device. Once you open Duo, you'll have to agree to Google's Privacy Policy and Terms of Service. From there, you can designate whether Duo can send you notifications and access your microphone and camera.

Once all that is done, enter your phone number. Google will send you a one-time code via SMS that you'll need to enter into Duo in order to verify your number. You must verify your number because your Duo contacts will use it to video call you, which is similar to how WhatsApp works.

You'll then be brought to the app's main interface: a screen that is split into two, with the top half showing you what your camera sees, and the bottom portion offering up a large video call button. When you first see this screen, you'll be asked to give Duo access to your contacts.

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Video calling

Every time you open Duo, you'll see the camera view/video call button screen. To start making a video call, tap the video call button on this screen (when you use the app later on, you'll also see quick-hit buttons for your recent and frequent contacts next to and below the video call button). A contacts screen will then pop up, from which you can search for contacts by name or number as well as invite friends to Duo. Your friends will need to install Duo for them to be able to video call you using Duo - which sounds obvious but is worth mentioning.

OK, so once a friend has Duo installed, hit the video call button, then find your friend on the contacts screen, and tap his or her name. The first time you call, Google will tell you "Smile! Knock Knock is on", along with a notice that says your friend - if he or she has you as a contact - will see you appear on their phone while you're ringing. In other words, don't assume your friend can't see you while you're ringing them, because they can, and that could lead to some embarrassing situations. (Your friend can't see you while ringing you, though.)

So, whenever you video call a friend, you'll see a screen that warns your video is a visible, then you'll see the name or the number of the person you're video calling, and an end button, all of which is superimposed onto a view of whatever your camera sees (likely you). When a friend calls you, and you happen to be using your phone, you'll see an incoming video call screen, which includes a view of whatever his or her camera sees, a name or the number of your friend, and buttons to either answer or end the video call. If you're not using your phone, you may simply get a notification that says a video call is incoming, but that depends on your notification preferences.

Once you answer a video call, or if your friend answers your call, you'll see the actual video call screen, which includes a view of whatever his or her camera sees and five buttons. These buttons include a button to change audio source, a button to toggle between your front and rear-facing cameras, a mute button, a button/round thumbnail of your camera view (which you can tap to enlarge and thus minimise your friend's camera view to the round thumbnail), and an end call button. It's all pretty straightforward, to be honest.

When you or your friend end a call, you will be brought back to the camera view/video call button screen, where you'll then see quick-hit buttons for your recent and frequent contacts next to and below the video call button. Keep in mind if you don't have someone in your contacts, the quick-hit buttons for your recent and frequent contacts will simply show their phone numbers, and tapping any of these number buttons will prompt you to either add the number to your contacts, start a video call, remove it from this list, or block the number.

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Manage preferences

While on the app's main interface (the camera view/video call button screen), tap the three-vertical-dots button in the upper right-hand corner. You'll then see options to go to Settings, Help, and Feedback. Tap the Settings option. Under this menu, there are several settings you can change, including the ability to turn off Knock Knock. You can also limit your mobile data usage, enable your phone to vibrate while ringing (Android only), unregister your phone number, and block numbers, among other things.

Yes. Duo is completely free to download and use.

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Yes. Duo has a feature called Knock Knock that lets you see live video of your caller before you answer. You can disable this feature under the Settings menu within the app (which we explain above in Manage preferences).

No. Duo is a 1-to-1 video calling app.

No. Duo needs your phone number. The app lets you reach people in your phone’s contacts list. No separate account is required.

Supposedly. Here's what Google has to say:

We’ve built Duo to be fast and reliable, so that video calls connect quickly and work well even on slower networks. Call quality adjusts to changing network conditions to keep you connected - when bandwidth is limited, Duo will gracefully reduce the resolution to keep the call going smoothly. For video calls on the go, Duo will switch between Wi-Fi and cellular data automatically without dropping your call. You can start your call at home, and continue seamlessly even when you head out the door.

Yes. Duo video calls are end-to-end encrypted.

Check out Google's announcement blog post.