Hello,
I have made one before..
I used the Android Emulator SDK (Android Virtual Device Manager) and used Camtasia to recored the screen.
Run your app in the Emulator then in Camtasia highlighted the area around the screen and recorded it.
Then I got a image of the phone and cut the screen part out using photoshop and placed the video inside the image.
Then you can create your own music, backgrounds etc.
I made one and here is how it turned out..
Demo Video
(in case you are wondering, the app allows you to control your alarm system from anywhere over Wi-Fi or 3G)