Under Construction & block other pages in CI

Hi friends,

I was searching in the forums to find how to create under construction page but i couldn't find any post that helps me to do this.

When I'm uploading my project on the host, something i need to down the website to do some uploads or maintenance. so i need to have a page to show to visitors like "under construction" page.. but the question is how to avoid of entering the controller/method to the url directly. I mean is even i set "Under construction" page as default controller, still users can enter some path to the url like (mywebsite.com/user/dashboard) .

How can i block securely all the pages during updating my app?

Thanks in advance.