auto-detect time settings like groups.drupal

Hi

I recently joined drupal groups, and after using my one-time login i changed my password and saved, leaving the time set to default +0000.

What I am interested in is the fact that when i went back to set my timezone to +1300, it was already set - automatically.

Does anyone here know what addin/module they use to do that?

Thanks in advance

Tracey