One of the scripts in my bag of tools to check whether a site is still up and running is content-check.pl. This little script compares the hash of a web page against a previously created reference hash. If the content of the web page has modified, this script will detect it and send an email.

You have to be very careful which page you check because even the slightest difference in the HTML source will be detected.

In Drupal you should not use any page that contains a form because each time the form is rendered a unique form id is generated and inserted into the HTML. This results in a different page hash and will cause the script to send an warning email.

Keep in mind that, if you have enabled the User login block, each page contains a small login form and is not a good candidate for monitoring through content-check.pl. You might have to resort to monitoring your update.php file instead.