A "knocker-upper" at work

The Knocker-Up (also referred to as a Knocker-Upper) gained prominence during the Industrial Revolution by using a long stick with wire or a knob affixed to the end to rouse customers at a desired time. Clients would agree verbally, in advance, or simply post a preferred time on doors or windows. For a few pence a week, clients could rest assured knowing their Knocker Upper would not leave until he (Knocker Ups were almost always men) was certain a person was awake. Larger Factories and Mills often employed their own Knocker Ups to ensure laborers made it to work on time.

Found at a Mental Floss article about how people woke up in the days before alarm clocks.