We use mobile alarm clocks, digital alarm clocks etc., but do we know how people used to wake up when there was no such thing as alarm clock. One thing people used to do was drinking plenty of water, as nobody can ignore the call of nature even in deep sleep. Next alarm clock for people was the annoying rooster's crow in the morning.
Then came the sundial which was not an alarm but a brilliant methodology to determine the time of the day using shadows cast by the sun. After that people used to rely on water clock which is another ancient method to determine the time.
Chimes of clock towers in the early 14th century, factory whistle for the workers all acted like alarm system for people to wake up at a specified time before the actual adjustable alarm clock came into existence. After this more inventions were made into the alarm system like the the snooze system.