check if session id exists

[Oaquasis]

I have a rather simple question, at least I think it is...

I want to check if a certain session id, that I stored in a database still exists. That way I can check if a user is still online and logged in, right?
I want to build a script which check who is currently online.

That's all.
I hope that someone can help me...

Oaquasis

[anthill]

Something like this?

<?
session_start();
if(!session_is_registered("member"))
{
 echo "Your still online you lazy f**k";
}

?>

Ant