Future Tense

Could Police Actually Shut Down a City’s Cell Service?

A protester shows a cellphone to a row of law enforcement officers.
A protest near the White House on June 3 in Washington. JIM WATSON/Getty Images

In the early hours of Monday, around 1 a.m., peculiar tweets began claiming that Washington, D.C., had been cut off from the digital world. A Twitter account with just three followers was the first to post about the supposed outage, the Washington Post later reported. By the time people began waking up and logging online, #DCblackout was trending in the U.S. The hashtag, which appeared in hundreds of thousands of tweets, was accompanied by reports of explosions, missing protesters, and silencers attached to police rifles. What followed was a brief period of online mayhem: Had the police really jammed cell towers? What was the alleged outage meant to obscure? Journalists on the scene quickly tweeted that they had not experienced any outages, and over the course of the day, the rumor was thoroughly debunked. The blackout, it turned out, was misinformation of the highest order. It was also a distraction from the realities of protesting on the ground, where police used violent tactics against protesters throughout the night, including pepper spray, rubber bullets, and tear gas.

The assumption of a blackout, though, presupposes that it’s possible for the police (or the federal government) to shut down communication networks entirely—an act with grave implications for free speech and the right to assembly, as well as for the safety of protesters and passersby. And although it didn’t take place on Monday, the hoax raised questions of whether it’s possible for law enforcement agencies to create a blackout—both technically and legally—and whether it’s likely.

Americans tend to think of deliberate service stoppages as dangerous tactics employed by oppressive regimes abroad. Jay Stanley, a senior policy analyst with the American Civil Liberties Union’s Speech, Privacy, and Technology Project, told me that communication shutdowns are generally seen as “an odious form of abuse”—something that’s used worldwide “as a way to cloak suppressive violence and other human rights violations.”

But this form of censorship has happened in the U.S. at least once. In 2011, the Bay Area Rapid Transit system, or BART, shut down cellphone service in underground stations in downtown San Francisco, after hearing of plans to protest the shooting of a man by BART police. BART’s goal was to prevent protesters from coordinating, but it was shortsighted, leaving the agency at the center of a national free speech controversy. The Federal Communications Commission got involved, and BART’s actions were condemned by rights organizations such as the Electronic Frontier Foundation (which referred to the incident as “BART Pulls a Mubarak in San Francisco”). The FCC investigated BART, but as Harold Feld, the senior vice president of nonprofit Public Knowledge, told me, the commission decided not to make a declaratory ruling on the incident. It came down to a technicality: BART had physically shut down the service by turning off equipment in the underground system, rather than jamming the signal.

No similar incidents have been confirmed since, but during the 2016 Standing Rock protests, Wired reported that tribal leaders believed police were jamming cellphones. The problem with proving these claims is that it’s difficult to tell whether something nefarious is happening or there’s just a bad signal. Only bodies like the FCC, which didn’t investigate the claims, really have the ability to verify that jamming has occurred.

The BART controversy and, to a lesser extent, Standing Rock show how complicated shutting down signals can be in the U.S.—and how we don’t really have a blueprint for understanding and addressing current and future blackouts by police departments. What we do know is that, nearly a decade later, it’s still possible from a technical standpoint. According to Joshua M. Pearce, a materials science and engineering professor at Michigan Tech, there are two main ways of creating a blackout aboveground. (The BART shutdown was an unusual situation, given that authorities could access the equipment themselves.) The first is to ask (or demand) service providers to turn off a particular set of cellphone towers. That’s as easy as flipping a switch, and providers generally want to comply with law enforcement.

The second—and far trickier—option is to use jamming technology, which sometimes works by sending out false signals that overpower those coming from a cellphone tower. Small-scale, short-range devices are available commercially from abroad (the kind that have been used, for instance, at certain universities abroad to prevent cheating, and that led to a Florida high-school teacher’s suspension in 2015). Theoretically, one could use a large number of small devices, like this one, to ring a neighborhood, but it wouldn’t be convenient. Jammers that cover larger areas do exist, Pearce said, but only organizations like the National Security Agency possess them.

The question of whether police blackouts are legal is much more complicated. The general rule is that it’s a violation of federal law to interfere with any wireless signal, according to Section 333 of the Communications Act of 1934, or the act that forms the basis of FCC policy. The FCC has issued public guidance stating that this applies to state and local law enforcement, and to Wi-Fi as well as cell signals. All jamming, in short, is illegal. However, Feld pointed out that local authorities could find workarounds that don’t involve jamming—like BART did. In theory, a service provider isn’t supposed to discontinue service without the FCC. But the Communications Act includes an exception for emergencies. So if the local police chief, for instance, went to phone companies saying “Hey, there’s a riot and we need you to halt your services for safety reasons,” the companies could choose to do that, in accordance with the law.

The greater danger, though, may come from the federal government. The FCC doesn’t regulate federal use and abuse of signals, so President Trump could order federal forces, such as the U.S. military, to jam signals or require that companies shut them down, Feld told me. He noted that the Department of Homeland Security, along with service providers, developed a protocol after 9/11 where the cellular companies will shut down their networks if requested by federal authorities. In addition, if Trump were to proclaim that there’s war, a threat of war, a “state of public peril,” or a “national emergency,” he would have the authority to act alone and essentially federalize and take over all means of communication, in line with the president’s war powers detailed in Section 706 of the Communications Act.

“[I]f Trump goes ahead with invoking the civil Insurrection Act, and he also invokes his powers under [Section 706], he could then arguably order phone companies to shut down their service on demand of federal authorities,” Feld said.

The president’s power as granted in Section 706 is so great that Jessica Rosenworcel, an FCC commissioner, called for a reassessment of it earlier this year. Congress, she said, should consider whether, in the digital age, this power is constitutional and how the other branches of government might temper it. Rosenworcel also said that the U.S. should finally develop policy on government-directed shutdowns. “Our existing law could be contorted to support outages, and we should expect to see government-directed shutdowns happen in many more places—including right here at home,” she said.

Perhaps it’s obvious that, legality aside, a blackout would endanger the public, and not just because of its clear violation of the First Amendment. “It’s the wrong response to political protests, whether it’s halfway across the world or here in the United States,” said Stanley. Service stoppages impede people’s ability to call 911 and check in with loved ones during emergencies, and they can disrupt health care and other businesses. “So by cutting off an entire mode of communication you’re not just stifling protests, you’re creating collateral damage that reaches far and wide,” Stanley said.

Whether a blackout seems distinctly possible depends on whom you’re talking to. Stanley was hesitant to speculate, though he thinks there are strong reasons to believe the U.S. won’t go that far again. “I think the BART incident was widely regarded by everybody as a mistake,” he said. But Feld is more concerned, even as he acknowledged that blackouts aren’t all that effective for the purposes of police or the federal government: They can disrupt protest coordination and affect live streams, but they can’t prevent individuals from taking videos and documenting their circumstances. Still, given the current environment, he’s worried. “The problem is that in a world where you’ve got police departments that are apparently willing to use tear gas … against unarmed protesters,” he said, “it’s not that hard to imagine they’re willing to jam cellphones.”

Future Tense is a partnership of Slate, New America, and Arizona State University that examines emerging technologies, public policy, and society.