UVB-76 is the callsign of a shortwave radio station that usually broadcasts on the frequency 4625 kHz (AM full carrier). It's known among radio listeners by the nickname The Buzzer. It features a short, monotonous buzz tone (help·info), repeating at a rate of approximately 25 tones per minute, for 24 hours per day. The station has been observed since around 1982.[1] On rare occasions, the buzzer signal is interrupted and a voice transmission in Russian takes place. Only three to four such events have been noted.
There is much speculation; however, the actual purpose of this station remains unknown.

The station transmits a buzzing sound that lasts 0.8 seconds, pausing for 1–1.3 seconds, and repeating 21–34 times per minute. One minute before the hour, the repeating tone is replaced by a continuous tone, which continues for one minute until the short repeating buzz resumes. Between 07:00 and 07:50 GMT the station transmits using lower power, when transmitter maintenance apparently takes place.

The Buzzer has apparently been broadcasting since at least 1982. as a repeating two-second pip, changing to a buzzer in early 1990. It briefly changed to a higher tone of longer duration (approximately 20 tones per minute) on January 16, 2003, although it has since reverted to the previous tone pattern

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