On the 5th February 1924 the BBC ‘pips’ were broadcast for the first time. Five short pips signal the five seconds leading up to the hour, with a slightly longer pip marking the start of the new hour. Although now largely inaccurate as a result of the inherent delay in the encoding, transmission, and decoding of digital radio broadcasts, the pips are still a part of many BBC radio programmes.
The BBC successfully broadcast the chimes of Big Ben for the first time at New Year 1924. This led the Astronomer Royal at the time, Sir Frank Watson Dyson, to suggest that time signals could be broadcast more regularly. Having convinced BBC boss John Reith, the Royal Greenwich Observatory fitted the pendula of two mechanical clocks with electrical contacts that sent a signal to the BBC every second.
The equipment that generated the pips moved from Greenwich in 1939, but the pips are still known officially as the Greenwich Time Signal. The name was even kept after the Greenwich Time Service stopped transmitting the pips in 1990. Since then, the national BBC stations have generated the pips themselves using an atomic clock in the basement of Broadcasting House.
Due to their use as a time signal, the BBC doesn’t allow programmes to broadcast the six pip sequence for any other reason, and used to strongly discourage broadcasters from ‘crashing the pips’ – that is playing any other sound at the same time. Although this rule is now less rigorously enforced on most stations, some Radio 4 listeners still wait with baited breath to hear a presenter accidentally talk over them.