Re-direct to mobile version upon loading on mobile device?

Is there a way to automatically redirect a user to a mobile version of the same site when trying to load the site on a mobile device?

That way I can create a sub-directory with the mobile version of the site and redirect users to that site upon loading on a mobile device.

Thanks for your support!

Or use one of the many responsive themes or frameworks. There is really no need to maintain a second mobile site anymore.