limiting the livetime of a session possible?

Hi there, I am building a user registering module and now I am wondering if there would be a way to destroy the session if the user was inactive for an specified amount of time. I found an article on that with following line: If you propagate the session ID via cookies, you can influence the cookies lifetime with the configuration value lifetime. Which configuration? I tryed session_set_cookie_params(10); But this is only valid for the same script. Does anybody have a good idea, or possibly a hint? Thanx for any help, Andy