Chances are you have one. You turn it to ALT before takeoff. You hit the IDENT key when requested. Whenever there is an issue with it though, you simply smile and nod along not wanting to let on to anyone that you have no idea how it actually works. In this blog on FunPlacestoFly.com, Anthony Arispe of Arispe Aviation, in McKinney, Texas, gives you all the information you need to figure out your transponder.
Source: http://generalaviationnews.comWhat is my transponder really doing?