When you say "page" do you mean "document"?
Or do you use jQuery Mobile, or some other library that lets you
Ajax-load multiple "pages" in the same document?
If not, then you cannot do it. Each document stands alone. You
cannot change something in a different browser tab. Each tab is
it's own universe, and cannot affect the others.
Maybe you mean you want your server to remember the alert state, so
that it either does or does not put an alert on pages that it serves.
If so, that's a server issue, and you'll have to find some
forum for your server language to help.