How to recognize a change in area on a site page?

Question

JavaScript

There is a site, beautiful, with a bunch of information, numbers and these numbers / values ​​are constantly changing. Some kind of stock market.
There is a certain area on the site where changes sometimes occur (change the order of several values ​​in rows). I want every 20-30 seconds. update the page, and if there is a change - get a notification by sound / mail.
The found Web services, even paid ones, offer such a detection at least once every 5 minutes, and this does not suit me.
Perhaps someone knows a service that can help me, or at least help me understand how laborious this question is (any solution, at least a simple page update-screenshot-comparison of the screenshot area with the previous version, with differences of for example 5-20% - an alert, even a separate computer is ready to allocate, just to simplify the solution)
PS I have not been a programmer for a long time .. so I ask for explanations at a level lower than you are used to :)

Answer 1

There are extensions for Chrome
https://chrome.google.com/webstore/detail/visualpi...
https://chrome.google.com/webstore/detail/page-mon...
https://chrome.google. com/webstore/detail/distill-...
and there are probably others.
I didn’t check the performance, but it’s stated that the last two can have a check interval of 5 seconds