stop code for X seconds, then continue

Question

How can I stop code for a few seconds and then continue?
I have a page in a navbar that only admins can enter. If you're not an admin, I want to have an alert of

You must be an admin to enter

And then the user will be Redirected to the home page. The code:

if (Session["user"] == null)
{
     Response.Write("<script>alert('You must be an admin to get into this page')</script>");
     System.Threading.Thread.Sleep(5000);
     Response.Redirect("index.aspx");
}

But whats happening is when I press the page in the navbar it waits five seconds and redirects me but never alerts me anything. Why is this happening?

Answer 1

You can use Response.AddHeader like this:

if (Session["user"] == null)
{
   Response.Write("<script>alert('You must be an admin to get into this page')</script>");
   Response.AddHeader("REFRESH", "5;URL=index.aspx");
}