*Really? Don't most people need an alarm or waking in some other manner?
People yes. Children no.*
The vast majority of people of any age with good sleep routines will not need an alarm or anything to wake them. The thing about good sleep routines though is it's not simply "go to bed earlier", it's about going to bed at the right time, going to bed too early makes it harder to sleep and changes the routine.
Sleep needs are a range, and children generally have a much wider range than adults, 11 hours of sleep (the OP's 9pm to 8am) is on the high side of that range, but the lack of waking naturally may suggest it's required - or it may suggest that the child is actually awake in bed but has decided to not get up for some non sleep need reason.
DD is 9, she is rarely asleep before 11pm and wakes naturally before 8am, this is still within the normal range of sleep needs for an eleven year old. I'm 46, I sleep with difficulty sometimes, but generally by 1am, but still always wake naturally with no alarm by 7:30 at the latest.
Teenagers particularly will often need an alarm, due to their natural sleep cycles often being later than is possible due to schools start time, that of course makes good sleep routines difficult.
It is possible that sleeping too much and not waking naturally is an indication of metabolic syndrome - there's a correlation between those who sleep outside the average and poor metabolic health. Like all metabolic syndrome causes, exercise is the easiest method to improve it.