They were probably too expensive, or not sufficiently reliable. > With the spread of electricity and affordable alarm clocks, however, knocking up had died out

They were probably too expensive, or not sufficiently reliable. > With the spread of electricity and affordable alarm clocks, however, knocking up had died out in most places by the 1940s and 1950s. > Yet it still continued in some pockets of industrial England until the early 1970s, immortalised in songs by the likes of folk singer-song writer Mike Canavan. The reason for that isn't clear.