PHP: Check if URL redirects?

I have implemented a function that runs on each page that I want to restrict from non-logged in users. The function automatically redirects the visitor to the login page in the case of he or she is not logged in.

I would like to make a PHP function that is run from a exernal server and iterates through a number of set URLs (array with URLs that is for each protected site) to see if they are redirected or not. Thereby I could easily make sure if protection is up and running on every page.

How could this be done?

Thanks.