Numbers stations are mysterious shortwave radio channels of indiscernible origin that exist in countries all across the world and have been reported since World War 1. They are identifiable by the unusual contents of their broadcasts: seemingly random sequences of numbers, words, letters, tunes, and Morse code, usually spoken by artificially generated voices of women and children.
The most common theory regarding the purpose of these bizarre stations is that they’re used by governments the world over to secretly transmit encrypted commands and messages to spies. That said, even though numbers stations have been discovered all over the globe and in any number of different languages, no government has ever officially acknowledged their existence. While the espionage theory is a logical one, with no official confirmation of their purpose the jury is still out.
One particularly odd station, UVB-76, has existed since the late 1970s and has broadcast a simple, repetitive buzzing tone 24 hours a day ever since. On very rare occasions, however, listeners have reported a Russian voice interrupting the buzz to read out sequences of numbers and words, always in a consistent format — this happened once in 1997, once in 2002, once in 2006, 56 times in 2010, and 14 in 2011. As with all numbers stations, its true purpose is and will probably remain unknown, but the increase in frequency of whatever it’s doing is certainly odd.
You can listen to well over 100 recordings of numbers stations for free on archive.org but be forewarned that they’re all kind of, well, eerie. They feel like something you shouldn’t be listening to, which stands to reason since apparently you’re not supposed to know they exist.