Pushing the button

Occupants of the Swan station followed a protocol in which they typed a sequence into a computer every 108 minutes. Typing these numbers and pressing "execute" (a.k.a. pushing the button) on the keyboard discharged an electromagnetic buildup, continually averting worldwide catastrophe.

The survivors discovered the station in November 2004 and spend weeks debating whether the protocol's meaning and consequences.

Countdown sequence

The timer began a countdown from 108 minutes.
With 4 minutes to go on the timer, an alarm was triggered at a rate of one beep every two seconds. The Numbers could then be entered, followed by the Execute key.
When the final minute was reached, a second alarm sounded at a rate of one beep every two seconds.
With 10 seconds remaining, the second alarm would speed up to a rate of one beep every one second.
When the timer reached 0, the timer flipped to a set of static red and black hieroglyphics, and "system failure" was broadcasted repeatedly over the station's loudspeakers.

Origins and purpose

Main article: The Incident (event)

The Swan was originally designed for experiments, but during construction, the DHARMA Initiative punctured the research site's electromagnetic pocket. A nuclear device also entered the pocket, further complicating matters. Following this incident, an electrical charge continuously accumulated at the Swan site. The Initiative designed the Swan protocol to discharge the amassed energy. An excessively large buildup could lead to a global catastrophe.

History

DHARMA Initiative

The protocol of pushing the button was set up after the Incident at the Swan site in 1977 when the DHARMA Initiative drilled into a pocket of electromagnetic energy on the Island. ("The Incident, Part 1") Exactly why the protocol was set up requiring constant attention by personnel at the station is unclear. A failsafe was also installed as a backup system - capable of destroying the energy pocket at the expense of the station and potentially the personnel stationed therein.

According to the Swan Orientation Film, DHARMA personnel were stationed in teams of two at the station for a tour of duty lasting 540 days. It was recommended that they work in alternating shifts in pushing the button. ("Orientation") At some point Kelvin Inman joined the DHARMA Initiative and was assigned to the Swan with his partner, Radzinsky. ("Live Together, Die Alone, Part 1")

After the Purge

Kelvin and Radzinsky were the only two known survivors of the Purge who did not defect to join the Hostiles. The two of them continued following the station's protocol until Radzinsky's suicide which left Kelvin manning the station alone - until he was joined by Desmond who crashed on the Island during his solo race around the world.

Kelvin introduced Desmond to the protocol - which he described as "saving the world." One night years later, while drunk underneath the Swan's computer room, Kelvin revealed to Desmond the nature of the Incident, and the function of the fail-safe key, which he carried at all times but was never able to find the courage to use. Desmond lived in the station for three years, until Kelvin's death. ("Live Together, Die Alone, Part 1")

Recent Events

Season 1

Desmond failed to enter the Numbers in a timely fashion on September 22, 2004, triggering a system failure. Although the sequence was entered just after the countdown expired, the resulting massive magnetic surge caused Flight 815 to break-up in mid-air and crash on the Island. ("Live Together, Die Alone, Part 1") ("A Tale of Two Cities") Alone in the Swan, Desmond continued to man the station for the next 40 days, carrying on the duty of pushing the button all by himself until the survivors blew open the hatch. ("Orientation")

Season 2

Jack and Locke were the first two survivors of Oceanic Flight 815 to learn of the station's protocol. Desmond, the lone caretaker of the station, disclosed the bare facts of the situation and pointed them to the orientation film. He fled the station after the computer became damaged in an accident, thinking it was destroyed. With Sayid's help, they managed to repair the computer - and Locke made a decision to take on Desmond's role pushing the button with the help of the other survivors. ("Orientation")

In "Man of Science, Man of Faith", a vision of Walt appeared to Shannon and spoke backwards "Don't push the button. Button bad". The meaning of this message is somewhat unclear; it was revealed later that not pushing the button was catastrophic. ("Man of Science, Man of Faith") ("Live Together, Die Alone, Part 1")

CounterZeroHieroglyphic — Bunker hieroglyphs

Days later, Locke inadvertantly allowed the timer to reach zero, at which time a loud sound was heard as if something were powering up -- and the timer then flipped to a series of red and black hieroglyphics. Locke discovered it was still possible to enter the Numbers and, on pressing Execute, the counter reset, flipping back to 108. ("One of Them")

Later, it appears a similar event took place off-camera, while Locke was trapped underneath the blast door. Ben (then still known as Henry Gale) claimed that he did not press the button, but given the catastrophic consequences of not pressing the button, it seems very likely that he was lying. ("Lockdown")

Following the DHARMA protocol, the survivors made an effort to set up shifts of two people in the station to operate the computer - with Locke initially taking on more shifts than anyone else. Locke's faith in the station, however, began to fall apart after Ben's arrival - and Ben's description of the Swan as a "joke." This feeling intensified for Locke after he and Eko visited the Pearl - when he came to view the protocol as a meaningless psychological experiment. Mr. Eko, however, took over the duty of pressing the button. ("Dave") ("S.O.S.") ("?")

The Season 2 finale revealed that the button serves as a discharge mechanism for an electromagnetic source within the sealed portion of The Swan. The incident, according to Kelvin, was a leak causing a "charge" to gradually built up over time. After 108 minutes, the increasing charge reached a point where the magnetic field began to have effects within the Swan itself. It was implied that if left unstopped, the magnetic field would continue to grow until it would destroy the world - or at least all life on Earth. ("Live Together, Die Alone, Part 1") ("Flashes Before Your Eyes")

After Locke destroyed the computer's monitor, the timer once again expired without the button being pressed. Although Desmond activated the failsafe, the resulting "event" (termed the discharge) was felt across the entire island, and resulted in the destruction of the Swan station. An electromagnetic pulse from the discharge interupted communication among the Others and also caused the failure of the satellite dish at the Flame. The discharge was also large enough to be detected at a tracking station in Antarctica. ("Live Together, Die Alone, Part 1")

Flash-sideways timeline

When Locke was recovering from surgery after he was hit by Desmond's car, Jack heard him mumbling "Push the button" in his sleep. ("The Candidate")

Other buttons

In "Meet Kevin Johnson", when Michael is trying to blow up the freighter he pushes a button marked "execute" in order to detonate the bomb.
In "The Lie", when Kate and Aaron enter the elevator, Aaron asks "Mommy, Mommy, can I push the button?"
In "Happily Ever After", when Desmond is undergoing a MRI-scan in the flash-sideways timeline, the MRI tech tells him he needs a button. When Desmond doesn't understand he explains: "The panic button. You need to stop, press it. Try not to 'cause we'll have to start all over again from the beginning."

Production notes

In Access: Granted, a special feature on the Lost: The Complete Third Season (DVD) Blu-ray edition, the reason for the numbers needing to be entered by humans and not by an automated process is explained:

Damon Lindelof: I think the idea of sort of trusting the machine, what if the power goes out, or what if the station gets taken over by the hostiles? You know, it absolutely had to be manned by human beings.

The producers later clarified that the turning of the key by Desmond prevented a potential "global catastrophe." ("Lost: The Answers")

Trivia

108 corresponds to the sum of the Numbers (4 + 8 + 15 + 16 + 23 + 42 = 108).
A short story by Richard Matheson (later turned into a 1980s Twilight Zone episode) called "Button, Button" deals with a couple that is given the option of pushing a button or not—with a surprising ending.
You can only push the button for 4 minutes, and as Desmond told Locke, it was to save the world. The Madonna song, "4 minutes", has a lyric that says, "We've got 4 minutes to save the world", which is oddly similar to the situation.
Pressing the button bears some resemblance to an episode of the new Outer Limits called "Dead Man's Switch" which deals with a group of humans who are locked in underground bunkers. The humans must press a button to prevent aliens from taking over the Earth but would allow the earth to be destroyed if they were dead.
The movie Sphere (based on the Michael Crichton novel of the same name) has a button that must be pushed every 12 hours. "Everything in the habitat is videoed, so every twelve hours we take the video storage out to the mini-sub and press the reset button. The idea is, if something happens to us and we don't reset it, the sub goes to the surface automatically, so if we're all dead, they at least have a partial record of what went wrong." There are also connections between the alien, time-traveling sphere in the story and Lost's Magic box.

Unanswered questions

Unanswered questions
Do not answer the questions here. Keep the questions open-ended and neutral: do not suggest an answer. More details...

For fan theories about these unanswered questions, see: Pushing the button/Theories

Why did the manifestation of Walt caution Shannon against pushing the button?
Why did the protocol use a code instead of just the button?