Webpage Update Notification
-- An advanced checker to notify changes occurred between visit

I would like to have a program which can keep track of different webpage. When the pages change, there is an alert/popup which will notify me. It is useful to track changes like new replies in particular boards, site news, version update news etc.

However the problem is a single unrelated change in a page would trigger the notification. For example, a random ad in the forum which will always trigger the alert. I wonder if the check can be more advanced. For example:
  • alert only when the selected part of the webpage is updated
  • decide the threshold on how many changes are needed to trigger the alert (helpful to prevent small unrelated changes from mis-triggering)


Do you have any program you can recommend?
I can pay for the program as long as it is powerful and suit my needs.