The Electronic Frontier Foundation (EFF) has launched Rayhunter, a free, open-source tool designed to detect cell-site simulators (CSS), commonly known as IMSI catchers or Stingrays. These devices, often used by law enforcement and intelligence agencies, mimic legitimate cell towers to intercept mobile signals, track user locations, and potentially eavesdrop on communications.
By making Rayhunter publicly available, the EFF aims to empower individuals and researchers to identify and expose unauthorized surveillance, shedding light on how extensively these covert devices are deployed.
How Rayhunter Works
Rayhunter focuses on detecting suspicious network activity without monitoring user traffic, ensuring privacy while identifying possible Stingray use.
The tool works by:
- Intercepting and analyzing control traffic—the signaling data exchanged between a mobile hotspot and the connected cell tower.
- Detecting anomalies such as forced downgrades to 2G (which makes phones vulnerable to attacks) or suspicious requests for a device’s IMSI (International Mobile Subscriber Identity).
- Alerting users in real-time when a potential Stingray attack is detected.
This approach provides a non-invasive method to identify potential threats without requiring advanced hacking knowledge or expensive equipment.
Affordable and Accessible Surveillance Detection
Unlike other Stingray detection methods that rely on rooted Android phones or costly software-defined radios, Rayhunter runs on a budget-friendly $20 Orbic RC400L mobile hotspot—a widely available 4G LTE router sold on Amazon and eBay.
EFF chose this hardware for several reasons:
- Low cost: Making surveillance detection accessible to a wider audience.
- Portability: A compact device that can be carried anywhere.
- Linux/Qualcomm compatibility: Potentially allowing Rayhunter to work on other devices in the future.
Rayhunter’s integration with the Orbic RC400L means that when it detects suspicious activity, the device’s screen changes from green/blue to red, visually warning users of a possible Stingray presence.
What Happens After Detection?
When Rayhunter identifies suspicious network behavior, it logs the events for further analysis. Users can access and download PCAP (packet capture) logs, which contain detailed network activity data.
These logs can be used to:
- Investigate possible surveillance attempts in specific areas.
- Contribute to forensic research on the spread of Stingray devices.
- Help civil rights groups and journalists uncover unauthorized tracking efforts.
EFF has made Rayhunter’s source code available on GitHub, allowing developers and researchers to review and improve the tool.
Legal and Safety Considerations
EFF has included a legal disclaimer, emphasizing that Rayhunter is likely not illegal to use in the United States. However, laws regarding IMSI catcher detection may vary by country, and users should consult a legal expert before using the tool in regions with stricter surveillance regulations.
BleepingComputer, a cybersecurity news platform, has stated that it has not tested Rayhunter and cannot verify its safety or effectiveness, meaning users should proceed with caution.
While Rayhunter is a significant step toward countering covert surveillance, it remains one piece of a larger digital privacy puzzle. Governments and law enforcement agencies continue to develop more sophisticated tracking methods, making it crucial for activists, journalists, and everyday users to stay informed about emerging threats.
