Comment 14 for bug 1251127

Simple mixer control 'Auto-Mute Mode',0
  Capabilities: enum
  Items: 'Disabled' 'Speaker Only' 'Line Out Speaker'
  Item0: 'Line Out Speaker'

the headphone Jack and line out Jack detection control return the state of the the Jack (plugged or unplugged)

pulseaudio use headphone Jack kcontrol to mute speaker volume

http://cgit.freedesktop.org/pulseaudio/pulseaudio/plain/src/modules/alsa/mixer/paths/analog-output-headphones.conf

[Element Speaker]
switch = off
volume = off

it also use line out front Jack kcontrol to mute speaker

http://cgit.freedesktop.org/pulseaudio/pulseaudio/plain/src/modules/alsa/mixer/paths/analog-output-lineout.conf

[Element Speaker]
switch = mute
volume = off