APscanner is a command-line tool designed for Apple's Airport Extreme Cards on Mac OS X to analyze wireless access points nearby.
It could be a useful tool which will help you to find access points while traveling or to analyze wireless problems, it also will advice you with a particular sound if an unencrypted wireless network is found.
APscanner minimum requirements are Mac OS X 10.3.9 or greater and an Apple AirPort Card (APscanner doesn't support any other wireless device).
It is console-based: this is useful when you need to boot Mac OS X in single user mode (or Darwin mode), which is text oriented, that means without any Graphical User Interface.
http://apscanner.sourceforge.net