Numbers stations are shortwave radio stations that broadcast computer-generated voices reading numbers, words, letters or Morse code. Their purpose has never been uncovered, but evidence from spy cases suggests that they're used to broadcast coded information to secret agents.

Over the past week or so, the output of one particular station that broadcasts from near Povarovo, Russia, increased dramatically. The station has a callsign of UVB-76, but is known as "The Buzzer" by its listeners because of the short, monotonous buzz tone that it normally plays 21 to 34 times per minute. It's only deviated from that signal three times previously -- briefly in 1997, 2002 and 2006.