it’s a wired FM mod, but made to only work on Sirius units. Every sirius tuner has an FM mod built right into it. 2 Years ago, after Howard Stern left FM, the FCC made Sirius lower the power output of their wireless FM modualtor. The reason being was that you could drive around NYC on a low band station and now hear Howard Stern, completely unedited. There were never any complaints until he switched over.