In Car/Portable Systems

Im am trying to figure out if the type of system I want exists....if anyone has any info it wouldbe much apreciated.

I had my car stereo stolen not too long ago so I am weary to put in another one. What I woul like is a small removable system such as some of the portable sat radio units that plugs into my car when im in it and basically leaves behind an empty dock when I take it with me.

Is there any product that simply has a dock that plugs directly into your car wiring (without a headunit) and doesnt leave behind anything that is worth stealing when you remove the unit??

Thanks for the info!