How Server notify me When SESSION or COOKIES is/are expired

I built by Website using PHP. I configured everything in website such as login, logout, register systems are already configured. I have Remember me check box in my login page that saves the encrypted login credentials in Cookie When user clicks it. These cookies will destroy after seven days. And I have SESSION start in every of my pages that tells user is logged in or not. My Question is When the SESSION expired I need it to notify user like giving alert for user. And the same on Cookies. How can I do that? Please help thank you.