How to disable microphone for OS X?
I know this is an old post, but the above command does not work. "tell application "System Events" to set volume input volume 0".  Sure, the slider moves all the way to the left, but if you make noise you can see the mic picking up input.  If you manually move the slider then it mutes.  Further analysis using the apple midi audio app indicates setting input volume to 0 via applescript actually sets it to 4.  I've tried putting in -4 and other negative values hoping it would work.  it does not.

I'm not sure why apple chose this behavior.  It has been the result of setting input to 0 via applescript that it is not really 0 for years now.  Very frustrating.