session expiry

[sturoy]

I am trying to expire a session when it a user has not use the site for a time, say 15 mins...

I have tried using something like this at the top of each page:

session_cache_expire(15);
session_start();

But that doesn't seem to do anything. Users who do nothing for 15 mins are still logged in.
Then I tried setting a timestamp in the session, and checking if that was less than current time + 15mins....

if ($_SESSION['time'] < time() + 900)
{
session_unset();
session_destroy();
}
session_start();

But this has 2 probs... firstly, if the user isn't logged in, there is no session to be destroyed! And secondly, you can't send things to the browser before calling the session_start.

SO..... is there an easy way to destroy a session after a certain amount of time? Because if it is automatically destroyed, then the next time the user loads the page, he/she won't be recognised. Bingo!

Any offers? Thanks in advance....
}

[LordShryku]

I usually use a meta tag to redirect after x amount of time to a page that logs out the user. You can just check if the user is logged in, if so, add the tag.