The box should say "chirp" on the outside. I think the other think you can do is look at the "setup" menu when you power on the unit. You will have a screen that tells you what software version you are running, etc and I think that screen also tells you if it is a "chirp" model. Worst case, if neither of those options works, call Humminbird with the serial number and they should be able to tell you if it is a chirp unit or not.
