Atama has created an elegant solution to protect sensitive information to prying eyes on your mac. A simple wireless dongle, the Sesame 2, uses proximity to automatically lock and unlock your Mac devices (beta testing for windows has begun) with parameters such as lock delay and locking distance and 3 levels of security.
Simply just walk away and Sesame will take care of the rest.
Unfortunately, Sesame has yet to cater for the Australian market. As such, a freight forwarder might be required if you wish to purchase the product at this time.
Price in Australia: AUD 50 + shipping