People made an early start in those days and so for a penny a week they could be roused by the long pole of the 'knocker-upper' tapping on the window at five o'clock in the morning. This figure played a very important part in the lives of the workers, seemingly never failing in the job, winter or summer.
Nellie Oldroyd - Knocker-uppers And Such-like
For many people, the morning routine begins with an unpleasant sound. In my case it is a loud incessant beeping from my alarm clock next to the bed. I am a man who likes his sleep and there are few things more annoying than that noise, and indeed, were I able to get along without it, my life would be all the happier. Unfortunately, it is a necessity without which I would routinely sleep the day away. This is probably the case for most people, we live lives by the clock and as such, the natural rhythms of the body are sacrificed at the altar of punctuality.
For our rural ancestors, life was different. Although amenities may have been scarce, and work hard, time was abundant. One lived from can till can't, and slept accordingly, burning the midnight oil only when necessity or whimsy dictated. More importantly, precision was not everything, the ground does not mind if it is tended half an hour later than usual, and livestock can usually spare the minutes waiting to be fed or slaughtered without much complaint. In Europe, only the church would require regularity, and their bells could be counted on to call the congregation to worship. Indeed, it is perhaps notable that the only people to really live according to strict hours were those who had taken the cloth.
This changed of course with the coming of the industrial revolution. Business began to work to quotas. Time became money and money was precious. Maximising production became everything. One can only imagine what those arriving in the big city from a country idyll must have thought. No longer could they work the hours dictated by the needs of the harvest, but by the greed of their masters and the wants of the new consumers. In particular, they would be expected to turn up to work on time, and tardiness could be harshly punished. It was to facilitate this that the job of knocker-upper was conceived.
"Mr Smalley, whom we called t’knocker-up man, came with his wire-tipped pole in the dark six mornings a week to shake our window. With his coming, Griffin Street began to stir. Daylight followed."
William Woodruff - The Road to Nab End
Generally found in the new industrial cities of the north of England, the knocker-upper's job was effectively the same as an alarm clock. At a pre-arranged time, they would knock on the sleeping person's window with a long pole tipped with a bristle of wires, stopping only when the individual was awake enough to shout that they were up. They would be paid for this service either by their clients themselves, or occasionally by a factory eager to ensure its workforce were not having a lie in on company time.
Quite how the knocker-uppers were able to get up on time is somewhat uncertain. Wikipedia tells us that they would rise early, suggesting 3am as an extreme, and another source mentions their grandfather having to rise at 4.30 for the job. Nevertheless, the absence of a more concrete source it's possible they simply stayed up and slept in the day. This was after-all the era that invented shift work, and presumably families and housekeepers could be relied upon to wake shift workers at the appropriate hour. That said, it seems a knocker-upper did not necessarily earn very much, (Tem42 tells me that in 1884 the Pall Mall Gazette gives a knocker-upper's price as tuppence a week) so presumably they had another income as well.
Of course, these days there are no more knocker-uppers. The very industrial forces that created them ultimately led to the mass-production of cheap or at least affordable alarm clocks. Reportedly, one of the last knocker-uppers was still doing the rounds in the second world war, apparently armed with what was effectively a pea-shooter instead of the traditional long pole. Their legacy has been fleeting; even the expression 'to knock up', known at least since the days of Pepys, is dying out thanks to the invasion of an American euphemism, and one-too-many embarrassing misunderstandings. It is still the case however, that in hotels particularly in the north of England, to ask to be knocked up in he morning still carries with it the meaning that it did to the workers in the industrial revolution.
http://en.wikipedia.org/wiki/Knocker-up and sources therein.