This was really more of an exercise to reproduce Brett's cough button but with Keyboard Maestro.
The cough button is comprised of two macros. There is a macro for the active button ("Cough Down") and the inactive state ("Cough Up").
The first macro watches for the keyboard state of ctrl-opt-cmd and Down Arrow to trigger.
When triggered, the macro grabs the current input volume and saves it to a Keyboard Maestro variable.1 It then runs a one line AppleScript to set the volume to zero. The rest of the macro provides some visual feedback with a Growl notification and a nice little red target in the center of the screen.
The real trick is turning the input volume back on when the hotkeys are released. That's straight forward. There's a KM trigger for that. Here's the macro to return the input volume to normal.
Again, there's a nice little Growl notification and visual target displayed in the center of the screen.
So, some fun with KM and a handy little microphone mute switch.
Remember, KM variables are system variable and are permanent. They persist through macros and even reboots. ↩