This gadget is a low-power FM transmitter that plugs into the 1/8th-inch headphone jack of any MP3 or portable CD player. I use the iRock with my iPod to play music over my car radio. I like it much better than those cassette adaptors that require you to keep a wire hanging out of your cassette player. I also use it with the boom box in my kitchen. The signal covers most of our house.