I prototyped a “breaking news” web alerts system for the Guardian, for our 2014 hack day. It won Overall Best Hack and is finally in production on the Guardian website. The alerts appear as animated overlays at the bomttom of the screen.
Their value is illustrated by a traffic graph for an example article, promoted using an alert. The red area show referrals from the alert, which features on any page in the edition that is being targeted (UK, US, Australia, or global.)
NB. The blue chunk shows referrals from the homepage.