disabling touch pad when mouse present

[David Berg]

What does "Removable Drives and Media Preferences" use for
"Automatically run[ning] a program when a USB mouse is connected?"

I'm looking to automatically disable my synaptics touch-pad while a USB
mouse is plugged in.  I know the commands that need to be run on mouse
connection and removal, where I run into trouble is how having the
command run when the mouse is removed.