A knocker-up or knocker-upper was a member of a profession in the Netherlands, Britain, Ireland, and some other countries that started during, and lasted well into the Industrial Revolution, when alarm clocks were neither cheap nor reliable. A knocker-up's job was waking people up so they could get to work on time. By the 1940s and 1950s, this profession had more or less entirely died out, although it still continued in some pockets of industrial England until the early 1970s. The knocker-up used a baton or short, heavy stick to knock on the clients' doors or a long and light stick, often made of bamboo, to reach windows on higher floors. In return for the task, the knocker-up would be paid a few pence a week. Some knocker-ups would not leave a client's window until they were sure that the client had been awakened, while others simply tapped several times and then moved on.

Source: Wikipedia