On Android, how to detect a system dialog is displayed (power options, recent apps, low battery...)?

I'd like to catch anything that causes the display of my Activity to get even partially hidden, e.g. power options, recent apps tray, low battery notification, etc... and I'm having a hard time to detect these system events.

I was pretty sure onPause() would be called when such events happen, but it seems to be wrong... or is it me?

Any other idea?... I'd preferably not hook on each system broadcast action individually, since I'd like to be as generic as possible (and react to ANYTHING that hides my Activity).