My mother is a shift worker. She works varying shifts at all kinds of ungodly hours.
Before she goes to sleep, she says to herself, 'I will wake up at 1am', and she concentrates very hard on it. She's never used an alarm in her life to my knowledge, and she tells me she's accurate, often to the minute. She says it just takes practice.
I know this works because I used to do it myself, back in the days when I still had something resembling a circadian rhythm. If you always go to sleep and wake up at the same time, it becomes an easy habit without an alarm.
I'm not very good at right speech, although I try, so please guide and correct me if necessary so I don't make bad kamma for myself and cause others to be annoyed. (=