Tech giant Google on Tuesday launched Duo, a one-to-one, end-to-end encrypted video calling app that is now available on Android and iOS devices.Duo is Google's take on other popular video calling apps including Apple's FaceTime, Microsoft's Skype and Facebook's Messenger app."In places like India, it has been designed to adapt to the network connectivity conditions. We hope to make the experience of video calling more personal, inviting easy and smooth", said Amit Fulay, Group Product Manager, Google, in a statement. To get started, all you need is your phone number and you will be able to reach people in your phone's contacts list across devices and platforms. No separate account is required so you can sign up and start calling in just a few taps. The "Knock Knock" feature allows people to see live video of the caller before they answer. For video calls on the go, "Duo" will switch between Wi-Fi and mobile data automatically without dropping your call, the company claimed.