Redirecting after session expires

I have a Redirect in my global.asax session start event, so when a user starts a new session they get redirected to the login page.

This redirect interferes with with other functionality.

How can I redirect a user back to the login page after they have
1) logged in
2) their session expires
3) and they click a button or menu??

Without the redirect in the global.asax the user just it just sits on that page when their session expires

Thanks
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