Ways to detect CTRL-N or when a user opens a new window

Question

How can we detect when a user opens a new window. The user is already authenticated and we make heavy use of sessions.

We were trying to avoid Ctrl+

Answer 1

You could possibly put a window count into the session and increment it on window.onload and decrement it on window.onunload.

Imagine me tutting, sucking air through my teeth and going "better you than me, guvna" if you use that, though.