EFF’s Rayhunter Empowers Public to Detect Covert Cellular Surveillance

The Electronic Frontier Foundation has unveiled Rayhunter, an innovative open-source tool designed to detect covert cellular surveillance tactics employed by law enforcement and malicious actors. This development aims to enhance public awareness and defense against unauthorized monitoring.

Rayhunter operates on an affordable Orbic RC400L mobile hotspot, enabling users to identify the presence of cell-site simulators , commonly known as “Stingrays” or IMSI catchers. These devices masquerade as legitimate cell towers, compelling nearby mobile phones to connect, thereby exposing users’ locations and potentially intercepting communications. The EFF’s initiative seeks to democratize the detection of such surveillance methods, making it accessible to individuals irrespective of their technical expertise.

Cell-site simulators function by conducting broad searches within their operational radius, capturing unique identifiers like International Mobile Subscriber Identity and International Mobile Equipment Identity numbers from all nearby mobile devices. Law enforcement agencies utilize these tools to pinpoint phone locations with remarkable accuracy, often circumventing the need for cooperation from telecom providers. Certain advanced models possess capabilities to intercept calls and messages, raising significant privacy concerns.

Despite their widespread deployment, the intricacies of CSS technology remain largely obscure. The lack of public knowledge about their functionalities and the specific exploits they leverage within cellular networks has been a persistent issue. Rayhunter addresses this gap by providing a means for the public to detect and document the use of such devices, thereby contributing to a broader understanding of surveillance practices.

The tool’s design emphasizes user-friendliness and affordability. By utilizing a readily available mobile hotspot device, Rayhunter allows individuals, including activists, journalists, and concerned citizens, to monitor their environments for unauthorized surveillance. This approach contrasts with previous detection methods that required specialized equipment or technical proficiency, thereby lowering the barrier to participation in surveillance detection efforts.

Rayhunter operates by detecting key indicators associated with cell-site simulators. These include attempts by a network to force a downgrade to less secure connections, requests for IMSI numbers, and efforts to disable encryption between the phone and the tower. Upon identifying such suspicious activities, Rayhunter alerts users, enabling them to take precautionary measures, such as turning off their devices, and logs detailed information for further analysis by security experts.

The introduction of Rayhunter is particularly timely, given the increasing reports of CSS deployment at public events and demonstrations. For instance, during the 2024 Democratic National Convention in Chicago, analyses suggested the likely use of such surveillance technology, raising concerns about unauthorized monitoring of protesters and attendees. The availability of tools like Rayhunter empowers individuals to detect and document such surveillance, promoting greater transparency and accountability.

EFF’s commitment to defending digital privacy and rights is further exemplified through Rayhunter’s open-source nature. By making the tool’s code publicly accessible, EFF encourages collaboration and continuous improvement from the global community. This openness ensures that Rayhunter can adapt to evolving surveillance technologies and remain a robust defense mechanism against unauthorized monitoring.

In addition to Rayhunter, EFF has previously developed tools like “Crocodile Hunter,” which utilized software-defined radios to identify unusual cellular activities. However, Rayhunter’s reliance on a simple mobile hotspot makes it a more accessible and cost-effective solution, broadening the scope of individuals who can participate in surveillance detection efforts.