Google added the record screen feature on devices running KitKat, and on the Xperia Z3 you can easily record the screen by following a few steps. To record screen on Xperia Z3 do as follows:
1. Press and hold the Power to open the pop-up window
2. On the opened window, tap the Record Screen icon
3. Read and accept the Legal Responsibility message, and a widget appears at the top of the screen
4. Tap the red record button to start recording the screen
5. You can also tap the second camera button to enable picture-in-picture recording (the screen and the front camera)
6. Tap the settings icon to change the video quality as well as the orientation.
7. Recorded videos can be found under this path: Internal Storage >> Movies >> ScreenRecords