We have only the vaguest idea where the broadcasts are coming from, and even less idea where they're going. The sounds are strange—the synthesized voices of women and children mixed with snatches of music, Morse code, or high-pitched buzzing. Sometimes the transmissions appear on a fixed schedule, other times in short random bursts. The only thing they have in common is the eerie recitation of numbers, beamed through shortwave radio signals bouncing across the globe.

These are the "number stations," which have mesmerized conspiracy theorists, radio enthusiasts, musicians and less obsessive members of the public for decades. They’ve been tracked with their own journal, recorded in an influential 4-CD set, and made appearances in lawsuits as well as a Cameron Crowe movie. No government agency has ever explained why they’ve taken over large portions of the shortwave radio dial, and why they’ve done so for years.

One of the most storied of the number stations is "The Lincolnshire Poacher," which began its transmissions with bars from the British folk song. Although it went off the air in 2008, number station detectives believe it was transmitting from a large military site in Cyprus. Another of the best-known stations, the Stasi-connected Swedish Rhapsody, started with a music box rendition of that tune before continuing with the voice of a little girl reciting numbers in German. A station known as the Magnetic Fields opened with the Jean-Michel Jarre's instrumental "Les Chants Magnétique" before broadcasting Arabic numerals and the English phrase "again, again."

The beginnings of the stations are unknown: by some accounts, the broadcasts first began during World War I, although better documentation exists for a beginning during the Cold War. While some suggest that they are the secret communications of drug smugglers, the more likely explanation involves espionage. Court cases, half-admissions, and the memoirs of ex-spies have brought the basics to light—the stations seem to be the broadcasts of intelligence agencies to their spies across the world. Messages are deciphered with a so-called one-time pad, in which a string of randomly generated numbers are mathematically added to text messages in order to encrypt, then subtracted to decrypt them. After each use, the pad is discarded.

While the use of number stations might seem startlingly low-tech for an espionage agency, their one-way nature has its advantages. Listening to the radio can’t be traced the way a telephone call can—because anyone can listen anywhere in the world, no one knows who the message is intended for. Listening to the radio isn’t a suspicious activity (the way carrying around expensive computer gadgetry might be) and doesn’t require much special equipment. Like the use of good old fashioned pen and paper, its simplicity is the key to its utility.

For years, public interest in the number stations was primarily limited to shortwave radio enthusiasts, who communicated with one another via online groups and magazines. A UK-based organization called ENIGMA (European Numbers Information Gathering and Monitoring Association), founded in 1993, tracked the transmissions with its own detailed newsletter for seven years. A radio hobbyist title called Monitoring Times Magazine also wrote about the stations, particularly through the activities of retired naval intelligence officer William Godby, alias Havana Moon. According to the Miami New Times, in the late 1980s Godby used signal-direction-finding equipment to pinpoint several number stations as coming from the "West Palm Beach airport, in nearby Tequesta, and at the Homestead Air Force Base. All were aimed at the Caribbean."

The name most often associated with the number stations today is Akin Fernandez and his Conet Project. In the early 1990s, the London-based Fernandez, who owns an indie music label, discovered the stations late one night while scrolling the dial with his new shortwave radio. When he discovered that no librarian or government agency could tell him what the number stations were doing, he became obsessed. The result, several years later, was a 4-CD set with samples of 150 different broadcasts, and an accompanying 74-page booklet. (Conet, a word Fernandez often heard on the broadcasts, is Czech for "end.") With the kind of treatment usually reserved for aging rock stars rather than secretive government broadcasts, the CDs became cult favorites—sampled by Wilco, who named its 2001 album Yankee Hotel Foxtrot after part of a numbers station broadcast, as well as other music groups, and appearing in the Cameron Crowe movie Vanilla Sky.

The Conet Project also prompted one of the first government admissions of the stations, when a UK government spokesperson told the Daily Telegraph in 1998: "These [numbers stations] are what you suppose they are. People shouldn't be mystified by them. They're not, shall we say, for public consumption."

Around the same time, Cuba’s "Atención" station became the world's first station publicly accused of broadcasting to spies. During a federal espionage trial following the 1998 arrest of the "Cuban Five," U.S. prosecutors claimed the spies were using hand-held shortwave receivers to listen to Atención broadcasts, entering the numbers into their laptops to decode the transmissions. The FBI testified that they'd broken into one spy's apartment and copied the decryption program, which they used to decode several messages. Three of the messages were revealed in court:

  • "Prioritize and continue to strengthen friendship with Joe and Dennis,"
  • "Under no circumstances should German nor Castor fly with BTTR or another organization on days 24, 25, 26 and 27,"
  • "Congratulate all the female comrades for International Day of the Woman."

And while some of the broadcasts might be just as banal as that last one, as Fernandez notes in the Conet Project booklet, part of the thrill of listening (the stations are still going strong) is that you have no idea what messages are being transmitted, or who else might be listening. "How many corporations are being compromised by mailmen who pretend to be listening to football results as they rifle through mail? And is the bus conductor on the no. 22 listening to the radio and writing down the results of the horses, or is he being told who his next murder victim is to be? Are all commuters really commuters? What is that buzzing?"