title: How do android "app lock" applications work?
body: <p>I've tried googling, and looking on stackoverflow as well, but I can't seem to find any satisfying answer as to how the "App lock" applications(eg: ZDBox, App Lock, etc..) work.
  Is there a service that runs in the background continuously polling to see if the app is launched and tries to kill it? Or is there a way to intercept launch intents for new activities?</p>