This comes from High Brow Magazine:
Many nights, Spooks turn on their shortwave radios and drift through the frequencies. On any given night, one can hear amateur radio stations broadcasting church sermons, utility traffic for aircrafts – with the right equipment, you can hear/contact the International Space Station. Yet one of the most eerie, mysterious uses of shortwave is that of the numbers stations: stations that feature ominous – sometimes robotic – voices saying seemingly random number patterns. Shortwave radio boomed in the 1920s: For decades, it was the only way to receive transmissions from far way.
Numbers stations, as they are called now, have been around since World War I, though many of the most famous transmissions took place during the Cold War. These mysterious stations are all, to date, unlicensed. Some feature automated voices, others have what sound like children’s voices, another with a sultry woman announcing numbers. One station – a Moscow-based broadcast during a Communist party coup – featured only the number five repeated for hours.
I KNOW! Keep reading. Then check out The Conet Project. While you do that, here’s a sample of a numbers station.