This invention offers an improved hands-free device for coupling to radio devices having mute and audio inputs. The invention couples serially between the radio and a portable electronic device such as a mobile telephone. The invention facilitates the delivery of appropriate audio signals to the radio. The invention also senses the activity of the portable electronic device and actuates a mute signal upon sensing such activity. The mute signal causes the radio to switch the input to its loudspeakers from a received signal to the audio being delivered by the invention from the portable electronic device. In so doing the invention offers an easy to install, inexpensive hands-free unit that takes advantage of the high fidelity loudspeakers in the automotive stereo system.