Webpage Update tool

I could not find an online tool available which gives alert whenever something changes on a particular page or post in a particular website. Do you know any tool which can do that ?

For example : if the site owner has updated his page by adding more content, how do i know without visiting their site.

Thanks in advance.

You can use for example chrome extension: PageMonitor although keep in mind that if u target pages or page parts that have dynamic content it will notice you about them. From online tools you can check out VisualPing or Versionista.

what about rss feed, that is updated. So subscribe to the site's rss and you'll be updated

Nice! This looks promising!