Get ClipCam
ClipCam runs on iPhone, Android and in the browser. The reaction videos you make sync to the same account across all of them.
On your phone
Install ClipCam: Reaction Video & Duo from the App Store or Google Play to record reactions with your front camera and publish to Duos.
In the browser
Use ClipCam on the web to react to a screen or a browser tab — screen reactions need a desktop browser that can share a screen.
The app is also searched for as Clip Cam and ClipCham; they all mean this app.