Applescript: display dialog until memory card is inserted

Question

I'm developing an applet to automate the process of copying video footage from my camera's memory cards onto my hard drive. It works perfectly, except that I cannot quit it. Here is the part of the code that needs help. It checks every 5 seconds for a memory card and, if one is inserted, continues to copy everything off it.
repeat
     set cardIn to 1
          with timeout of 86400 seconds
                    tell application "Finder"
                              repeat while cardIn is 1
                                        if exists disk "EOS_DIGITAL" then
                                                  set cardIn to 0
                                        else
                                                  delay 5
                                        end if
                              end repeat
                    end tell
          end timeout
     (the rest of the code)
end repeat
The problem is that there is no way I can find to quit once it is in this wait loop. The menu command to quit and the Command-Q hotkey both do nothing so I have to force quit when done. What I'd like is to be able to have a dialog displayed asking this user if they want to quit while it's waiting, but I don't know how to do that without it having to "give up after 5 seconds". That makes a new dialog display again every 5 seconds when it rechecks for memory cards, which would get very annoying for anyone using the computer.
I wish something like this would work...
repeat until (list disks) contains "EOS_DIGITAL"
     display dialog "Waiting for card..." buttons {"Quit"}
     tell me to quit
end repeat
...but it still waits for a button to be clicked in the dialog. I want this to be a truly automatic process, where plugging in a memory card triggers the whole copy process (which is already done and works perfectly) so I would rather not have to click a button to continue.
Is there any way to have a dialog displayes with a quit button that automatically goes away once a memory card is inserted without using "giving up after x seconds"?

Answer 1

Keeping a script or application locked up inside delays or repeat loops will keep it from responding to system events.  There are a few ways to monitor when a volume gets mounted:
Write your application using AppleScript in Xcode to watch for a workspace notification;
Use launchd or a folder action to watch the /Volumes folder (an alias is added to the folder when a volume is mounted);
Make your script into a stay-open application and use an idle handler to periodically check.