Intercepting the back button
Simply override the onKeyDown(int, KeyEvent) method in your activity and look for the back button. Return true so that the event is consumed.
public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_BACK) { //Do something here return true; } return super.onKeyDown(keyCode, event);}
As schwiz pointed out, you'll want to override the onBackPressed() method in your activity class (http://developer.android.com/reference/android/app/Activity.html#onBackPressed()).
I just wanted to add that if you did want to at some stage continue with or access the standard the back operation (after say, displaying a dialog), then you simply call super.onBackPressed() or ActivityName.super.onBackPressed() from anywhere in the Activity.