 Until November 2010, the buzz tones lasted approximately 0.8 seconds each.One minute before the hour, the repeating tone was previously replaced by a continuous, uninterrupted alternating tone, which continued for one minute until the short repeating buzz resumed, although this stopped occurring in June 2010.The Buzzer has apparently been broadcasting since at least 1973 as a repeating two-second pip, changing to a buzzer in early 1990.