Then I tried different Paper Signals on my Servo. I tried to build an umbrella on it and when a new file added, the umbrella will be open. While the paper is not easy to fold so it is ok when the new file adds to Drive and the umbrella is open but it is weird when no file added and the umbrella is folded. 

So I change the idea into an icon shows 'new file in Drive' and the servo will change the cover when the function are called. See the video below.