Help with session variables!

[alfieshooter]

I have a problem I'm sure should be easy to solve.

Basically, I have a chat window which pops up when clicked from a parent window. When a user does this I want their status to change to 'online', so I make an entry in a database.

When the user closes the chat window I want their status to change to 'offline', so I need to make a deletion from the database.

I have it working using a combination of PHP and javascript, but I not happy with it.

What I want to be able to do is set a session variable from the chat window, which will expire when it is closed down.

However, what I don't know how to get around is, if the user keeps the chat window open, but closes the main parent window (which I would have used to refresh and check if the session was still active), then how do I know when the user closes the chat window, as the parent has been closed so I have nothing to check if the session is still active.

Is it possible?

Please help.

Thanks