Detecting connect on call transferred via auto-attendant

I am building an automated call system that is supposed to play a message when the person being called answers the phone. This works fine for DID numbers since I can detect when the person answers the phone and then start playing the message. However, I need to handle the situation where the person being called is transferred to via auto-attendant. I can detect when the auto-attendant answers the phone and send the appropriate DTMF tones to dial the extension, but how can I then determine when the extension is answered?

This is not a normal way of imlplementing and automated attendant. You need to tell us much more about your configuration.

I am currently in the conceptual/prototype phase of my development and have a prototype built that plays a pre-recorded message when the outbound call connects to the destination number.

I am trying to come up with a solution that will work when the destination of the outbound call is an extension handled via an auto-attendant. When the auto-attendant answers the call, my plan is to transmit DTMF tones to tell the auto-attendant the extension to which the call should be forwarded. What I am trying to figure out is if it is possible for my calling system to determine when/if the person at that extension answers the phone? If it is possible, how would I go about doing it?