Unity3D Android Back Button Best Practice
Google has done extensive analysis and focus group research on Android user behavior. One important issue that Google research has identified for Android developers is to always have a listener for the Back button. It seems that Android users become angry or irritated if the application or game ignores the back button. In Unity3D simply add the following code into your loop:
if (Input.GetKeyUp("escape")) { // Quit application Application.Quit(); }