In Sapiens, on p. 354 of my copy:
During World War Two, BBC News was broadcast to Nazi-occupied Europe. Each news program opened with a live broadcast of Big Ben tolling the hour – the magical sound of freedom.
Ingenious German physicists found a way to determine the weather conditions in London based on tiny differences in the tone of the broadcast ding-dongs. This information offered invaluable help to the Luftwaffe. When the British Secret Service discovered this, they replaced the live broadcast with a set recording of the famous clock.