Drupal 7 has a feature to display a maintenance mode page when you are working on your website. Users can see only maintenance message “Use the site in maintenance mode” when maintenance mode is enabled. Admin
can access entire Website.
Log into the Drupal 7 Dashboard.
Go to Configuration > Maintenance mode.
Make sure the "Put site into maintenance mode" box is checked.
Enter the message you want visitors to see during the interruption.