Some radios simply require grounding out their mute wire, while other radios may require applying +12V to thier mute wire. I haven't tested the mute wire of my 9500ci, but I bet that when the 9500ci alerts the green wire gets +12V applied to it and that the other copper colored wire gets grounded. I will have to test this in order to verify it. Also, if Escort's engineers were smart, I am sure that the 9500ci's mute wires are current limited to protect the 9500ci electronics from damage should the +12V green wire accidentally get grounded or if +12V is accidentally applied to the copper colored ground wire. I will try to get an answer from Escort about this stuff -- either that or I will test it myself.