This seemingly simple combination of a car charger bulb and detachable iPod cable actually hides a few interesting features.
The iPod cable, shaped to fit an iPod nano but physically compatible with all Dock Connecting iPods, includes a pass-through port on its bottom for use with other third-party accessories, such as FM transmitters.
It can detach to let you charge any USB device, such as an iPod shuffle or cell phone, assuming you have the right USB cable.