To automatically run the program on device plug in or plug out events, add this to udev
rules:
ACTION=="add", ATTRS{bInterfaceClass}=="03", ENV{DISPLAY}=":0.0" RUN+="/bin/su - <YOUR USER HERE> -c /usr/local/bin/touchpad_disabler"
ACTION=="remove", ENV{DISPLAY}=":0.0" RUN+="/bin/su - <YOUR USER HERE> -c /usr/local/bin/touchpad_disabler"