"Shortwave numbers stations are a perfect method of anonymous, one way communication -- spies located anywhere in the world can be communicated to by their masters via small, locally available, and unmodified shortwave receivers," reads the Web site of The Conet Project, an outfit that's compiled 150 numbers stations recordings from the last three decades on a four-CD set. (The word "Conet" is the sign-off signal on one station.)

And that's the short of it. For 30 years, intelligence organizations have allegedly broadcast one-way messages to their agents in the field via shortwave and the transmissions happen to sound weirder than any Stockhausen score or minimalist electronica you've ever heard -- a child's voice, or the obviously synthesized intonation on what's known as the "Lincolnshire Poacher" station, named for the folk song accompanying the numbers.

"Alleged" is a key word here when talking about the numbers stations' purpose, even though it seems that everyone with their ear to the airwaves is in agreement as to the stations' spy connection. A rare mainstream media article about numbers stations published in the Daily Telegraph last year quoted a spokesman for the Department of Trade and Industry, responsible for regulating the airwaves in the U.K.: "These [numbers stations] are what you suppose they are. People shouldn't be mystified by them. They are not for, shall we say, public consumption."

But when I wandered into Aquarius Records in San Francisco's Mission District, how could I not consume? While I began browsing through the improv-jazz works of John Zorn, the electro-acoustic ontology of Terre Thaemlitz and the surreal soundtracks of Ethiopian field recordings, I barely noticed the sounds emanating from the store's stereo -- a computer voice calmly rattling off digits. Likely a new release, I thought, from Robin "Scanner" Rimbaud, the British composer who injects snippets of electronically eavesdropped cellular phone calls into his mixes.

The numbers continued to flow through my brain as I shopped, though, present enough to be distracting but not repetitive enough to be annoying. Call it mutant Muzak. After 20 minutes, I found myself and the clerk in deep conversation about "The Conet Project: Recordings of Shortwave Numbers Stations," one of the store's "staff favorites." Like the clerk, I was hooked on the bits of Conet lore that were spread like a cultural virus by the Aquarius employees and customers. Probably unlike him, I dropped $60 to analyze the Conet CDs in the comfort of my home.

My preferred dose? One CD of Conet before bedtime. Repeat if necessary. Be warned, though: Side effects may include grainy and nihilistic nightmares starring a grayscale spy cabal armed with an arsenal of dead media. Conet as soundtrack to a J.G. Ballard noir documentary. Indeed, Ballard's style of (non) fiction blends seamlessly with the blurb on Conet's stark, minimalist packaging: "The origin of these stations is in dispute. Their purpose is unclear. Some of these organizations should have been closed down after the 'end of the cold war,' yet they continue to transmit like clockwork."

And therein lies the mystery that keeps headphones on hundreds of numbers listeners around the world. Most of these people aren't the avant-audio enthusiasts who frequent Aquarius. They don't know from musique concrete. These shortwave buffs are knob-twiddlers of a different sort. For them, the process of numbers stations is more interesting than the product. Under the mainstream radar, numbers stations Web sites, online chat rooms and e-mail lists thrive with listeners sharing frequencies, recordings, rumors, stories and speculations about the strangest sounds on the dial.

"If you tune in to the BBC World Service, you know where the studios are, who the intended audience is and where the transmitters are, but with numbers stations you don't know any of that," says Simon Mason, a chemistry lab supervisor in England who in 1991 penned one of the first texts detailing the numbers racket, "Secret Signals: The Euronumbers Mystery." "It's like a mystery novel or television show, but the difference is no one will ever come out with a solution."

Mason was a teenager twiddling the knobs on his father's shortwave set in the early 1970s when he was first caught in the numbers trance.

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