From a lonely rusted tower in a forest north of Moscow a mysterious short wave radio station transmitted day and night. For at least the decade leading up to 1992, it broadcast almost nothing but beeps; after that, it switched to buzzes, generally between 21 and 34 per minute, each lasting roughly a second -- a nasal foghorn blaring through a crackly ether.

Enigma: The mystery of Russia's UVB-76 radio transmissions explored