AppleScript to toggle the input device (microphone) volume between 0 (muted) and set volume

input_volume.osa

on run
	set vol_level to (input volume of (get volume settings))
	
	if (vol_level < 1) then
		set volume input volume ReadVolumeLevel()
	else
		set volume input volume 0
		WriteVolumeLevel(vol_level)
		return vol_level
	end if
	
	return vol_level
end run


on WriteVolumeLevel(volume_level)
	try
		set open_volume_file to ((open for access (POSIX path of (path to home folder from local domain) & ".mic_level") with write permission))
		set eof of open_volume_file to 0
		write volume_level to the open_volume_file starting at eof as «class utf8»
		close access the open_volume_file
		return true
	on error
		try
			close access file open_volume_file
		end try
		dialog("failed")
		return false
	end try
end WriteVolumeLevel

on ReadVolumeLevel()
	try
		set volume_file to (open for access (POSIX path of (path to home folder from local domain) & ".mic_level"))
		set vol to first paragraph of (read volume_file for (get eof volume_file) as «class utf8»)
		close access volume_file
		return vol
	on error
		return 100
	end try
end ReadVolumeLevel

The script can be used as an Automator Quick Action and activated with global shortcut (set in System Preferences) or from the Services menu. Check the "Ignore this action's input" in the Run options.