Using a listener to detect data from an external application

could anyone please let me know how to detect when variables are sent through to a Flash movie from an external application? i have tried to set up a listener but so far have only managed to activate it on mouse or button events.

the external application (designed by a third party) sends variables to the main timeline. i need a listener to detect when these variables arrive, so i can update dynamic text fields.

if you need any clarification, i can supply the relevant information.

thanks in advance