(The man or woman used a 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 and would not leave a client's window until they were assured they were awake. Obviously the job no longer exists, but the fabulous job title was "knocker upper".
Great Expectations, by Charles Dickens, includes a brief description of a knocker-upper.
The phrase "knocked up" entered British slang as a term for "being awakened", but don't use it, as it now takes the American meaning "to be made pregnant".)