>I don't have a mute line connected

Exactly. And neither do nearly all of the rest of us. Which makes it perfect for home dock detection for (almost) everyone. The nice thing about that line, is that it can be read rather simply -- it's just a pin. Tuner detection requires much much more, including an actual tuner in the vehicle..

I'm thinking of perhaps tying the mute to the serial TX line (through a resistor, perhaps), and then just strobing the serial and reading back from the mute. That way, it could be used by everyone, even those who actually have the mute line connected up to a cellphone/onstar/whatever in their vehicle.

Cheers