Google Maps API navigation event listener (turn left, etc.)

I want to extract google maps turn-by-turn navigation events in my own application.

How can I expose the functionality of the Google Maps API that I can get a listener for events like turn left or right events.

I embed GMaps nicely in my app, or just listen to any event where Gmaps is normally routed and my app is in the background.

I googled but didn't find anything useful ...

Bye and thanks