How to incorporate app_offline into web application to prevent access?

Hello Community

    In Sharepoint 2010 Server in the web application from Site Actions I selected
New Page and named it app_offline and entered html code to state that
the site is under maintenance in the html source icon on the Ribbon.

    While saving the text the message stated it was being saved in Site Pages.

    But when I went to another computer and typed in the web application url
I still got the web application.

    The question is since "app_offline" is supposed to prevent users from accessing
a web application page during maintenance why did the web application page still
appear when its url was entered instead of getting the app_offline page?

    Thank you
    Shabeaut