Alarm sounds in Dharma barracks, Richard Alpert strides out of jungle

While Sawyer tells the group about his conversation with Horace, the alarm sounds in the Dharma barracks indicating that someone has broken through the perimeter. Security officer Phil comes and tells the group to get inside. They enter one of the houses where a woman named Heather watches out the window while holding a gun. Sawyer and Juliet watch from one of the windows and see Richard Alpert confidently and angrily stride out of the jungle. He jams his torch into the ground and both Sawyer and Juliet look concerned.

This is the same alarm we heard in "The Man Behind the Curtain" in season 3 when young Ben and Annie are in class.