Detect when an ejectable device is (un)plugged in OS X

Question

I am wondering how to be notified when a mass storage device is plugged (or unplugged) to the Mac.

Answer 1

If you're writing a Cocoa app you can register for NSWorkspace notifications that fire when disks are mounted or unmounted.

At a lower level (more appropriate if you're writing a daemon or NSWorkspace doesn't give you enough information) you can use the Disk Arbitration Framework.