I'm not sure it's even the correct action to do within your app. Most of the time there is going to be more than one way to launch an activity even within an a

I'm not sure it's even the correct action to do within your app. Most of the time there is going to be more than one way to launch an activity even within an app. So going up can ruin the user experience even within your app. The only time I see a reason to override the back button is in games. When playing a game you don't want the back button to accidentally bring you back to the main menu screen. Most override the button and either ignore it or bring up a pause menu. In non-game apps overriding it just causes problems. I've also seen apps override it when they choose to have a lot of different functionality in a single activity. This is poor app design.