who is on the page?

Hi everybody, I've been looking for a script to determine who is on my page (people have to log in). So far, I've been using a script that updates the time in the database continuously as long as the person is on the page. That way, the script could determine whether the user is still online or not. However, this script has way too many queries and uses too much server resources. Is there anything else? I'm wondering if the connection_status() function would help in any way... thx, Olli