Check for change UIAlertview

I need a little help programming an iPhone/ipad alert. I want it to alert the user (even if the app is running in the background) at any time if a specific website is changed (in this case a blog). I think this will effectively alert the user if a new blog post is published. I want to control this alert from an on/off switch. does any one have some sample code? or at least a point in the right direction.