Available for Android and iOS, Duo does not require a user to have a Google account. Instead, the app is tied to a phone number. It is meant for one-one-one conversations and doesn’t allow for group calls.
To start a video call on Duo, users just tap the other party’s number. Google says Duo is easy to use, fast and has a reliable connection. The app’s Knock Knock feature lets users see live video of the caller before they answer.
"Knock Knock makes video calling more spontaneous and welcoming, helping you connect with the person before you even pick up," the app’s principal software engineer, Justin Uberti, wrote on Google's official blog.
On the security front, Uberti said all Duo calls are end-to-end encrypted, while users can flip between WiFi and cellular networks without dropping a call.
An Engadget review compared the app’s look to Apple’s FaceTime app, where users see the person they are talking to while their own video feed shows up in a small circle.
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