Helping set up for the [AUPN](http://www.apertureprofessional.com/) launch party this weekend, I needed to load files onto 100 USB flash drives for the obligatory [swag](http://en.wikipedia.org/wiki/Swag) bag. To churn through it efficiently, we had an Automator workflow copy the files onto the drives. All I had to do was insert a drive, double-click the workflow app, wait until it copied the files and unmounted the drive, then unplug the drive.
After doing this a few times, it seemed silly having to manually run the workflow; I wanted it to run automatically when a drive was plugged in. Fortunately, the solution came to me in a flash (pun absolutely intended).
It occurred to me that a [folder action](http://www.apple.com/applescript/folderactions/) should detect not only files, but also devices. When you mount a drive, what folder does it appear in? Your instinct may say "the Desktop," but this is a Finder illusion. In fact, mounted drives appear in the invisible root-level directory /Volumes/.
Thus, I saved the workflow as a folder action plug-in for /Volumes/, and it worked perfectly. All I had to do was insert a flash drive, wait for the workflow to finish, remove the drive, and insert another one – 100 times.
Here are the steps:
1. Go to *File > Save As Plug-in*.
2. Choose *Folder Action* from the pop-up menu.
3. In the *Attach to Folder* pop-up, select *Other...*
4. In the resultant open dialog, hit *cmnd-shift-g*. This will bring up a small sheet labeled *Go to the folder:*.
5. In this sheet, type `/Volumes/`, and hit the *Go* button, then hit *Open*.
6. Hit the *Save* button in the Plug-in sheet.
With this trick, any mounted device will trigger the attached workflow. What that workflow does is up to you, but the possibilities are endless.