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Sonar fence
[[{{{Video}}}|Orientation Video]]
First seen
Last seen
Constructed by
Controlled by
Discovered by
A keypad is used to enable the fence. The actual keypad is a HID model RKL55.
The Monster cannot pass the sonar fence. ("Left Behind")

The high-frequency sonar fence is a continuous stream of high-intensity sound waves generated by a series of evenly-spaced pylons surrounding the Barracks. It was built by the DHARMA Initiative. ("LaFleur-Enhanced") The range of the waves reaches only as high as the top of the pylons. ("Par Avion") With the potential to render someone walking through the fence unconcious, or even killing them, the waves can cause severe cerebral hemorrhaging to humans who pass through them. Although humans can physically breach the barrier before the sonic waves trigger side effects, the Monster cannot pass between the pylons while the fence is active. ("Left Behind")

The sonar fence was first mentioned in the DHARMA Initiative Barracks video, seen by Ben Linus when he first arrived on the Island. The film described the fence as serving to protect the Barracks area from the Island's abundant wildlife. Ben encountered the sonic barrier as a child, while running out of his home. He later obtained the code to deactivate the sonic barrier and, as a test, sent a rabbit through the barrier before crossing it himself. ("The Man Behind the Curtain")

Kate, Locke, Sayid and Rousseau encountered the sonar fence on their mission to rescue Jack. According to Mikhail Bakunin, their prisoner, and the DHARMA cabling map discovered by Sayid in the Flame, the fence extends all the way around the area containing the Barracks. ("Par Avion")

The fence can be set to a lethal level.

Locke appeared to kill Mikhail by shoving him through the barrier. ("Par Avion"). After passing through it, he began shaking violently, foaming at the mouth, and bleeding from the ears. He collapsed on the ground and appeared to have died. However, Mikhail did actually survive, and later helped save Naomi after encountering Desmond and the others who were attempting to find her. ("D.O.C.") After he returned to the Others' camp, Ben commented, "I thought you were dead." Mikhail responded, "I am fortunate the pylons were not set to a lethal level." ("The Man Behind the Curtain")

After seeing what happened to Mikhail, Locke, Kate, Sayid and Rousseau made a ramp out of a tree trunk in order to scale the barrier and bypass it. In doing so, they did not break the connection between each barrier pylon, which Sayid guessed was the trigger for the sonic waves. ("Par Avion")

As shown by Ben in his flashback, the barrier can be deactivated. Kate and Juliet encountered the inactive fence while running from the Monster. After crossing to the other side, Juliet entered the code 1623 into a data pad, and after lifting a panel and turning a knob, the fence was reactivated. The Monster then attempted to attack the pair, but was repelled by the sonar fence, which appeared to act as a physical barrier against the smoke. After the Monster retreated, Juliet explained, "We don't know what it is but we know it doesn't like our fences." ("Left Behind")

When a young Ben deactivated the fence, he used the code 54439. This code was changed every day according to the orientation film he and Roger watched upon arrival to the island. The fence intensity seems to be controllable at a continuous scale going from red to green to black, where green is presumably a repelling but less harmful effect. ("The Man Behind the Curtain")

The fence was seen in excellent condition after the final skip in time of the Island. Juliet shouted for Daniel to immediately stop as he almost walked through it. Amy faked disabling the fence by using earplugs. Sawyer, Jin, Miles, Daniel and Juliet walked through the fence, which rendered them unconscious. Richard Alpert managed to get past the fence, and claimed that his people could do so with ease. ("LaFleur")

Early warning system

Locke answers the system's phone call. ("The Shape of Things to Come")

The early warning system, created by the DHARMA Initiative, warns the residents of the Barracks via an automated telephone call that consists of a woman's voice repeating "Code 14-J". The system is activated when a panic code is entered to disengage the sonar fence.

In the extended version of the Barracks video, new DHARMA members were instructed how to disarm the sonar fence. They also received an explanatory leaflet from Security. [1][2] "14-J" was their code for trespass of a Hostile on DHARMA Initiative territory, in violation of the truce. ("Namaste")

Alex activated the early warning system after being kidnapped by Martin Keamy and the mercenary team. Forced at gunpoint to deactivate the fence, she entered the panic code 1623, initiating the warning phone call at Ben's house in the Barracks. ("The Shape of Things to Come")


A fence seen in "The Moth"
  • Juliet mentions "fences" in the plural possibly hinting of other similarly protected facilities on the Island. ("Left Behind")
  • A notation near the top of the blast door map states "DHARMA Protocol- No stations past security barrier".
  • In Season 1, a fence can be seen in the distance. It is likely a real fence in Hawaii that was accidentally filmed. ("The Moth")
  • There are keypads or control panels on both sides of the fence. ("The Man Behind the Curtain")
  • A deleted scene from "The Economist" involved Miles, without any apparent knowledge of the sonar fence, correctly detecting that the fence was inactive.
  • One way to bypass the fence is by taking the tunnels underneath the Barracks. Another is to climb directly over the top of the pylons. ("Par Avion")  ("Follow the Leader")

Unanswered questions

Unanswered questions
  1. Do not answer the questions here.
  2. Keep the questions open-ended and neutral: do not suggest an answer.
More details...
For fan theories about these unanswered questions, see: Sonar fence/Theories
  • Why is the Monster unable to pass through the fence?
  • How do the Others bypass the fence?

This article uses material from the "Sonar fence" article on the Lostpedia wiki at Wikia and is licensed under the Creative Commons Attribution-Share Alike License.


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