Do not regenerate session_id

[eluser]Agustín Villalba[/eluser]
Hello!
I'm developing an application which needs to check if a user has been logged in from 2 diferent navigators/computers and avoid it. For that, I need to check the session_id of the user, but CI changes the session_id every 5 minutes, so I don't know if the user has 2 sessions in the application or it's only the regenerated session_id of CI.
How can I make this? If I have to prevent the regeneration of session_id in CI, how can I avoid that?
Thank you very much.