A monotone voice cut through the static on a new shortwave frequency: “Tavajjoh! Tavajjoh!” followed by a string of numbers. The encrypted transmission, intercepted and described in a federal government alert sent to law enforcement agencies, prompted a familiar question for many who heard of the message and its timing — what are sleeper cells, and could the broadcast be an activation signal?
What Are Sleeper Cells? How did authorities characterize the transmission?
The alert describes a likely encoded sequence relayed across multiple countries shortly after the death of Ayatollah Ali Khamenei, who was killed in a U. S. -Israeli attack on Feb. 28. The message was encoded, destined for clandestine recipients who possess the encryption key, and has the hallmarks of a transmission intended to instruct covert operatives or sleeper assets without using the internet or cellular networks. The alert says the transmissions could be intended to activate or provide instructions to prepositioned sleeper assets operating outside the originating country, while also noting there is no operational threat tied to a specific location at this time.
Could a number station-style broadcast be an operational trigger?
Federal authorities flagged the new broadcast as reminiscent of old number-station tactics: an automated voice reading numerals that operatives with a key could translate into instructions. Law enforcement has long recognized that such encrypted, shortwave methods can serve as triggers for deep-cover operators. The alert calls for increased monitoring of suspicious radio-frequency activity and heightened situational awareness because the sudden appearance of a new station with international rebroadcast characteristics is unusual.
“Sleeper cells have always been a concern when it comes to Iranians and their proxies, ” said Horace Frank, former head of counterterrorism for the Los Angeles police and a retired assistant chief. He warned that, given current operations and strikes, some proxies and sympathizers could feel more desperate — a reminder of why authorities treat these signals seriously even when no specific target has been identified.
How are institutions and communities responding to the risk?
Federal counterterrorism bodies have placed increased emphasis on vigilance. The Department of Homeland Security and the FBI are described in the alert as operating at elevated readiness, with a memo to local police agencies calling for heightened watch. The alert instructs law enforcement agencies to increase monitoring of suspicious radio-frequency activity and to remain alert to anomalous signals that could match the transmission’s characteristics.
Beyond technical monitoring, the broader law-enforcement response reflects past experience: the Department of Justice has pursued individuals allegedly involved in plotting attacks or hiring assassins in the United States. The DOJ charged Shahram Poursafi, identified as a member of the Revolutionary Guard, with attempting to hire people to assassinate a former national security official in U. S. locations. Public accounts by a former Secretary of State noted earlier efforts by Iran to enlist operatives abroad and the degree to which would-be attackers sometimes conducted surveillance of homes and offices.
At the same time, investigators emphasize caution. Counterterrorism officials have so far found no credible specific threat tied to the new broadcast. The alert explicitly states that while the contents cannot currently be determined, the signal’s emergence warrants heightened situational awareness rather than immediate alarm.
The human dimension is evident in communities with large military or government populations, where the escalation of strikes and retaliatory rhetoric has sent a chill. Officials working on monitoring and analysis must balance that community concern with measured, technical responses: tracking radio-frequency anomalies, cross-checking encrypted broadcasts, and coordinating with local agencies to monitor suspicious activity.
Back on the shortwave bands, the male voice’s numeric cadence remains an unresolved puzzle. The transmission’s style evokes Cold War techniques but surfaced in a modern conflict context after the Feb. 28 killing of a foreign leader. For residents and officials alike, the question lingers: what are sleeper cells capable of now, and how will signals like this be handled to prevent harm?
The static fades but not the unease. The alert has prompted steps in monitoring and local readiness that aim to translate technical detection into protective action, even as investigators work to decode the transmission and determine whether it was intended as an operational trigger or something less ominous. The shortwave broadcast that opened this story remains a pointed reminder — and the country watches and listens, waiting for clearer answers to what are sleeper cells and whether any have been set in motion.
