On the 5th February 1924 the Royal Greenwich Observatory began broadcasting the hourly time signals known as the Greenwich Time Signal (GTS). It is popularly called the “pips” and is a series of six short tones broadcast by many BBC Radio Stations
The BBC had already started transmitting the bells of Big Ben, on New Year’s Day 1924. This led the Astronomer Royal Sir Frank Watson Dyson, to suggest that time signals could be broadcast more regularly. So he convinced BBC Director John Reith and the Royal Greenwich Observatory fitted the pendula of two mechanical clocks with electrical contacts that sent a signal to the BBC every second.
Since they are used as a time signal, the six pip sequence cannot be broadcast for any other reason, and the BBC used to strongly discourage broadcasters from ‘crashing the pips’, i. e. playing any other sound at the same time.