Agricultural labourers, who worked by the sun and the seasons, wouldn't need artificial assistance to wake up, but factory work went by the clock.

I gather that in industrial towns, there was a lad employed as a `knocker up', who went round all the houses with a rapper on the end of a pole to knock on workers' windows to wake them up in the morning in time to get to work. (I can't remember where I heard of ths, nor have I met anyone who claimed to have been knocked up themselves, so it may be an industrial myth.)