Possible Duplicate:
PHP /SESSION: Login one per user?
I need to know how to let one user login once.
Possible Duplicate:
PHP /SESSION: Login one per user?
I need to know how to let one user login once.
If you are using PHP's built in sessions feature. You can get the Session's ID using $session_id = session_id();
When a user logs in you could take the session id that it generates and store it into a database under that user's account. Then on each page check to see if the current Session ID matches the one stored in the database for that user (If not, kill the current session and redirect them to a sign in page).
The session id will be different on each device they login using.
Does that make sense?