It's the tape adapter for your iPod which "senses" the button presses on your tape player--that is, FFW=hitting next on your iPod, REW=previous, etc etc. Seems like an awesome idea and I was excited (since I've always been using a tape adapter to listen to my iPod in the car). Problem is, after trying it in 2 different cars, the POS doesn't work. In my Acura TL, it freaks out, fast forwards a couple of times, and eventually ejects the tape, never producing any audio whatsoever (keep in mind, I've used a number of other tape adapters in my car, all of which work w/o any difficulties, so it's not my tape player's fault). In a Lexus ES330, you can hear audio, it play/pauses the iPod when the tape player goes on and off (as it should), but FFW and REW don't do anything beyond spinning the tape (the iPod just keeps playing...but you don't hear it)! I was hoping it was just a defective unit, but based on the different performance in each car, it just looks like defective engineering.