Early this morning, residents of Hawaii received an emergency alert on their cell phones and on their television screens: “BALLISTIC MISSILE THREAT INBOUND TO HAWAII. SEEK IMMEDIATE SHELTER.” If that wasn’t enough to spark panic in a state where Cold War-era nuclear-attack alert sirens have been undergoing testing, the warning ended with those five dreaded words: “THIS IS NOT A DRILL.”

Following several minutes of panic and confusion, various authoritative sources confirmed that the alert had been sent in error. Hawaii Congresswoman Tulsi Gabbard took to Twitter to say that she had “confirmed with officials” that there was no ballistic missile threat. U.S. Pacific Command (PACOM) issued a statement noting that the “Earlier message was sent in error,” and that the State of Hawaii would issue a correction. Thirty-eight minutes after the original alert, a second followed: “There is no missile threat or danger to the State of Hawaii. Repeat. False Alarm.” Russian, Chinese, or North Korean intercontinental ballistic missiles (ICBMs) could make it to Hawaii in less than 38 minutes, mind you.

This is, to be clear, a catastrophic error. It quite justifiably undermines the American public’s confidence in the emergency alert system (EAS) and the competence of government authorities. Given President Donald Trump’s emotional volatility and unitary nuclear-launch authority, paired with North Korea's breakneck technological developments on its ballistic-missiles and nuclear-weapons programs, nuclear anxieties are higher today than at any time since the end of the Cold War. A false alarm, as a result, can inflict serious and undue psychological stress, particularly for Americans already feeling quite vulnerable to an ICBM-armed North Korea.

False alarms of the apocalypse are not a new feature of the nuclear age. Governments have long sought to notify citizens of an incoming nuclear attack. During the Cold War, with the ever-looming, terrifying prospect of nuclear war with the Soviet Union, the U.S. government established an extensive educational and organizational effort to facilitate so-called civil defense—an effort to provide the public with the knowledge it needed to cope with an eventual nuclear attack.

Fortunately, to this day, nuclear weapons have been used just twice, at Hiroshima and Nagasaki in the closing days of World War II. As a result, few public-emergency alerts warning of nuclear attack have been issued in the United States. When they have, they've been false. The U.S. public has mostly been spared the anxiety and helpless anguish of a false nuclear-attack notification. But there have been exceptions.

In February 1971, the North American Aerospace Defense Command (NORAD) issued a teletype notification to every American radio and television broadcaster warning of an impending thermonuclear war. It later had to retract the message. Information moved slower at the time from government authorities to the American public; broadcasters largely did not pause their programming to relay the entire message.

In the wake of Saturday’s incident, it will be important for the Pentagon, the Hawaii government, and the Department of Homeland Security, to investigate what went wrong and offer a full public accounting. There are numerous possible explanations. None are particularly reassuring.

According to Governor David Ige of Hawaii, the error occurred during a change of shift, when an “employee pushed the wrong button.” Whether intentional or not, if this was the result of a single point of human failure, then it can be written off as a bureaucratic and command failure, with the individual or individuals reprimanded; the country can move on, hopefully with the confidence that lessons have been learned and a repeated can be prevented.

A spokesperson for the Hawaii Emergency Management Agency told The Atlantic that the erroneous alerts were issued during a “shift change,” when “somebody clicked the wrong thing on a computer.” The spokesperson added: “We needed a cancellation procedure. So basically we’re going back and checking all of our processes. We’re aware that our credibility is vital. We’re doing everything we can to reassure the public that this was a one-time error, that it will not happen again.” While the situation is still bad, this is actually the best possible outcome—especially considering the alternatives.

Consider one alternative: An attacker managed to penetrate the Hawaii EAS and issue a false alert. (“No hacking,” the Hawaii Emergency Management Agency spokesman told The Atlantic, emphasizing that the incident was caused by “human error.”) But this possibility is still among the more unsettling scenarios—and it’s far from unthinkable. In September 2017, U.S. military personnel and their families in South Korea received false mobile alerts instructing them to evacuate the Korean Peninsula—an alert that would be among the most-reliable indicators of impending U.S. military action against North Korea. U.S. forces in South Korea later clarified that they hadn't sent the alert, and U.S. counterintelligence opened an investigation. That investigation is ongoing.

Issuing a false alert of an impending ballistic-missile strike through a legitimate EAS may be among the most pernicious forms of “fake news.” At a time when state and non-state actors alike are resorting to disinformation operations, it’s all the more important for the U.S. government to ensure the inviolability of critical communication systems like the EAS. The Hawaii and South Korean incidents at least have an important point in common: Both exploit common fears about a possible scenario involving North Korea.

One more possible alternative—and perhaps the most worrisome, from a nuclear-stability point of view—is some sort of system-sensor error, involving a critical flaw in the network of sea-, ground-, air-, and space-based sensors operated by the United States military. While at this point this doesn't appear to be the case with the Hawaii incident, given that NORAD, Strategic Command, or PACOM did not corroborate the EAS alert, this long used to be the kind of nuclear false alarm scenario that Cold War decision-makers had to wrangle with.

After the end of the Cold War, former National Security Adviser Zbigniew Brzezinski told the harrowing tale of his famous “3 a.m. phone call” in 1979, when he was awoken by an aide informing him of an incoming Russian nuclear attack. He had only minutes to decide whether to tell President Jimmy Carter. On instinct, Brezinski nearly moved to order bombers to ready for a retaliatory strike, before realizing the alert was likely false. Indeed it was: a NORAD exercise tape was mistakenly interpreted as real, giving the appearance of an all-out incoming Soviet strike. (On the Soviet side, a man named Stanislav Petrov, a lieutenant colonel in command at a facility monitoring for incoming attacks, would have to make similarly fateful decision in 1983.)

These kinds of false alarms and “near misses” involving nuclear decision-makers didn’t end with the Cold War, either. In January 1995, Russian President Boris Yeltsin was informed of what appeared to be an American ICBM headed for Moscow. Russian nuclear forces were alerted and Yeltsin was given the Cheget (the Russian "nuclear football") before learning that the incoming missile was, in fact, just a Norwegian rocket on a trajectory that, on Russian early-warning radars, appeared quite similar to an American ICBM.

While nothing like what Brzezinski, Petrov, and Yeltsin faced took place on Saturday, both the Hawaii incident and these so-called “near misses” are a reminder of the dangers—psychological and physical—we invite by allowing nuclear weapons to persist in the world.

The real reason nuclear weapons have been used only twice against human populations and never again may have little to do with the compelling logic of nuclear deterrence, and far more to do with luck; the world has come close to nuclear apocalypse repeatedly and a strategy the relies on this luck never running out might require reassessment. Consider, for instance, if President Trump, instead of spending his time on the green at Mar-a-Lago’s golf course (per pool reports), instead had seen reports of an attack on Hawaii and issued a valid retaliatory order.

Mistakes happen with emergency alert systems and they can happen with real nuclear weapons. For the residents of Hawaii who felt unexpected dread and helplessness looking at their phones on Saturday morning, that'll be all too clear.