On Friday, more than 60,000 people packed into Rio’s Maracanã stadium for the opening ceremony of the 2016 Olympic Games — but above their heads, something disconcerting was happening. Observers reported as many as three drones hovering above the stadium, triggering a security panic that reached all the way to the teams providing protection for visiting heads of state. It was the exact scenario Brazilian security had hoped to avoid — but despite the latest equipment and months of preparation, keeping drones out of an open-air stadium is still an extremely difficult job.

Behind the scenes, Brazilian authorities have taken bold new steps to keep drones away from designated Olympic areas, but not all of the new measures are effective. The country has partnered with drone manufacturers like DJI to update the onboard software with Olympic geofences, preventing drones from flying in the forbidden areas. But not every manufacturer has taken up the self-imposed limits, so to stop other drones, the Brazilian military has purchased new devices to jam drone-control signals in mid-flight. These jamming devices required the telecom regulators to grant the military new legal authorities over the civilian airwaves. It’s an aggressive step, and one that many observers worry could lay the groundwork for cell-service blackouts after the games have finished.

New devices to stop drones in mid-flight

Ultimately, the drones above the stadium dispersed on their own, but the military had other systems in place if they didn’t. A recent Vice report found the Brazilian military has purchased eight DroneBlocker devices from a company called IACT, motivated by concerns from the 2014 World Cup in which one team was accused of spying on practice sessions with a drone. The DroneBlocker devices work by blasting incoming drones with radio signals, effectively jamming the signal from the controller. Typically, drones will hover to the ground after losing contact with the controller, at which point they can be safely recovered — although in the case of the opening ceremony, that would have dropped the targeted drones right into middle of the stadium.

The army also obtained new legal powers in order to use the devices, which has raised significantly more controversy. On February 1st, Brazil’s national telecom agency officially authorized the armed forces to jam radio signals during the Olympic games. Crucially, the authorization made no reference to drones specifically, leading many observers to worry the same authorization could be used to stifle the anti-Olympic protests that occurred in advance of the games.

"Blocking signals, even during an emergency, just prevents people from getting access to emergency services," says Deji Olukotun of Access Now, which has urged Brazilian authorities not to block internet access. "It sows confusion, and we’ve seen time and time again that that kind of blocking often precedes human rights violations."

"It sows confusion"

Service blackouts have become a common way to stifle protest actions, from the local 2012 blackout of service in San Francisco’s BART system to the string of nationwide internet shutdowns that occurred during the Arab Spring. So far, there’s no indication of those tactics being used in connection with the Olympic Games.

The devices purchased by Brazil are part of a range of anti-drone measures that have gained traction as police grapple the public safety implications of unmanned aerial vehicles. There are a number of different methods for bringing down a drone in mid-flight, including intercepting and hacking into the control signal itself, but jamming is still the most reliable. In the US, that power is limited to federal agencies, since state and local law enforcement are subject to the FCC’s anti-jamming provisions.

Still, activists are concerned that the same powers used to keep drones out of the Olympics could be put to far worse purposes in the future. "Once the army has this technology," Olukotun says, "we have no knowledge of the limits on how it can be applied."

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