A device capable of intercepting phone signals was likely planted 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 station simulator, was identified by the Electronic Frontier Foundation (EFF), a digital rights advocacy organization, after analyzing wireless signal data collected by WIRED during an event in August.
Cell simulators mimic cellular transmitters to intercept communications, indiscriminately collecting sensitive data such as call metadata, location information, and application traffic from all phones within range. Their use has drawn criticism from privacy advocates and activists, who argue that such technology can be used to secretly monitor protesters and suppress dissent.
The DNC met amid widespread protests over Israel’s attack on Gaza. While authorized influencers attended exclusive yacht parties and VIP eventsthousands of protesters faced a large presence of forces of orderincluding officers from the US Capitol Police, the Secret Service, Homeland Security Investigations, local sheriff’s offices and the Chicago Police Department.
Concerns about possible surveillance prompted WIRED to investigate the first wireless survey of its kind to investigate whether cell simulators were deployed. The reporters, equipped with two rooted Android phones and Wi-Fi hotspots running detection software, used Rayhunter— a tool developed by the EFF to detect data anomalies associated with these devices. WIRED reporters monitored signals at protests and event locations across Chicago, gathering extensive data throughout the political convention.
Initial tests conducted during the DNC did not reveal conclusive evidence of cell simulator activity. However, months later EFF technologists reanalyzed the raw data using improved detection methods. According to Cooper Quintin, senior technologist at EFF, the Rayhunter tool stores all interactions between devices and cell towers, allowing for deeper analysis as detection techniques evolve.
The breakthrough came when EFF technologists applied a new heuristic to examine situations in which cell towers asked devices for IMSI (international mobile subscriber identity) numbers. According to EFF’s analysis, on August 18 – the day before the convention officially began – the device carried by WIRED reporters on their way to a hotel where Democratic delegates from states in the US Midwest were staying suddenly switched to a new tower. That tower looked for the device’s IMSI and immediately disconnected—a sequence consistent with the operation of the cell station simulator.
“This is extremely suspicious behavior that normal towers don’t exhibit,” says Quintin. He notes that the EFF typically only observed similar patterns during simulated and controlled attacks. “This is not 100 percent irrefutable truth, but it is strong evidence to suggest that a station simulator was set up. We don’t know who is responsible – it could be the US government, foreign actors or some other entity.”
Under Illinois law, law enforcement agencies must obtain a warrant to set up cell simulators. Similarly, federal agents—including those from the Department of Homeland Security—must secure warrants unless there is an immediate threat to national security. However, the 2023 DHS Inspector General report found that both the Secret Service and Homeland Security Investigations did not always comply with these requests.