Sup is an easy to setup web application for Node.js that will ping your urls and warn you by email if their HTTP status code changes.
You can find a demo here.
Installation & Support
You can use this app for one website for yourself or for one client. You can adjust the source of the app to meet your needs. If you want to use this app for a service or include it in a product you can contact me for batch licenses at email@example.com.