A device capable of intercepting phone signals likely was deployed during the 2024 Democratic National Convention (DNC) in Chicago, WIRED has learned, raising critical questions about who authorized its use and for what purpose.
The device, known as a cell site simulator, was identified by the Electronic Frontier Foundation (EFF), a digital rights advocacy organization, after analyzing wireless signal data collected by WIRED during the August event.
Cell site simulators mimic cell towers to intercept communications, indiscriminately collecting sensitive data such as call metadata, location information, and application traffic from all phones within range. Its use has drawn widespread criticism from activists and privacy advocates, who argue that such technology can be exploited to covertly monitor protesters and suppress dissent.
The Democratic National Committee met amid widespread protests over Israel’s attack on Gaza. As reputable influencers attended exclusive yacht parties and VIP events, thousands of protesters faced a strong police presenceincluding agents from the U.S. Capitol Police, Secret Service, Homeland Security Investigations, local sheriff’s offices and Chicago police.
Concerns about possible surveillance led WIRED to conduct a wireless survey, the first of its kind, to investigate whether cell site simulators were being deployed. The journalists, equipped with two rooted Android phones and Wi-Fi hotspots with detection software, used lightning hunter—a tool developed by the EFF to detect anomalies in the data associated with these devices. WIRED reporters monitored signs at protests and event venues across Chicago, collecting extensive data during the political convention.
Initial testing conducted during the Democratic National Committee did not reveal conclusive evidence of activity in the cell site simulator. However, months later, EFF technologists reanalyzed the raw data using improved detection methods. According to Cooper Quintin, senior technologist at the EFF, the Rayhunter tool stores all interactions between devices and cell towers, allowing for deeper analysis as detection techniques evolve.
A breakthrough came when EFF technologists applied a new heuristic to examine situations where cell towers requested IMSI (international mobile subscriber identity) numbers from devices. According to EFF analysis, on August 18, the day before the convention officially began, a device carried by WIRED reporters on the way to a hotel hosting Democratic delegates from Midwestern US states. abruptly changed to a new tower. That tower requested the device’s IMSI and then immediately disconnected, a sequence consistent with the operation of a cell site simulator.
“This is extremely suspicious behavior that normal towers don’t exhibit,” says Quintin. He notes that the EFF typically observed similar patterns only during simulated, controlled attacks. “This is not 100 percent incontrovertible truth, but it is strong evidence suggesting that a cell site simulator was implemented. We don’t know who was responsible; “It could have been the US government, foreign actors or another entity.”
Under Illinois law, law enforcement agencies must obtain a court order to deploy cell site simulators. Similarly, federal agents, including those at the Department of Homeland Security, must obtain warrants unless there is an immediate threat to national security. However, a DHS inspector general in 2023 report found that both the Secret Service and Homeland Security Investigations did not always meet these requirements.