In calendar, or iCal if you don't have Mountain Lion, make a new event, then right click the event and click get info. uncheck 'all day' if it is. put in the time. put repeat every day or custom if you want. then next to 'alert', put message with sound then click the sound you want. then put on date, and insert the time again.

There's quite a few apps in the app store like 'Wake Up Time' but as far as I'm aware they'll only work if your mac is not in Sleep mode.

Thanks Matt, most helpful and clear to follow.

Much appreciated.

will the alarm still go off while my macbook pro is closed?

System Preferences/Energy Saver - set sleep to never.

cool, thanks!

This works. Thanks!

But Apple should really stick an option right up there in the Date and Time on your actual computer to let you add an alarm. Lots of us get absorbed in work and would like a quick way to just have the computer remind us to stop on time!

Send Apple feedback. They won't answer, but at least will know there is a problem. If enough people send feedback, it may get the problem solved sooner.

Feedback

I would like to see this sort of functionality but in a different form. Something quick like set alarm built into iCal or just built in to the clock menu item/menu extra. Sending feedback now.

Rather than setting sleep to never, which could reduce the screen-life and wear on the internal hardware of the device, it would be more optimized to set the device to wake out of sleep at a certain time, like a few minutes before your calendar alarm is set to go off.

SystemPreferences_EnergySaver_Schedule_StartUP/Sleep_Ok

Hopefully Macs will eventually feature a simple alarm system for everyday consumer needs and lifestyle; most of which will involve requiring the machine to wake up in order to sound the alarm. Simple human necessities are often overlooked in the process designing complex architectures that cater to conspicuous features.

Wake Up Time - Alarm Clock

By Rocky Sand Studio Ltd.

Open the Mac App Store to buy and download apps.

amen!

This has really helped - thank you Ali

Thanks for the suggestion! I downloaded this app & it did the trick.