We saw this alarm bug all the way back in the first edition of PocketPC.
"Wakeup Tweak is a little program that corrects a bug that appeared in Windows Mobile 2003 concerning alarms that don't always ring when they should. Everyone knows now that the PocketPC turns itself on at midnight to execute some maintenance routines, in particular the alarm initialisation. There is a fault in that the delay to switch on the Pocket PC is only 15 seconds, and that that time lapse is too short to do it correctly. Consequently, some users had have the unpleasant surprise of not hearing their Pocket PC ring out when it should have. This bug can be corrected by a change to the Registry, but if you are not too inspired to do this, you can install this utility instead." I say it mitigates the issue because the above registry tweak doesn't fix the problem 100% of the time. I've seen posts in the newsgroups that by changing the 15 seconds to 60 seconds, it greatly increases the chances you'll get the alarm, but doesn't guarantee it. Still very odd that I have no problems at all on my 2215, the device most people with the alarm issue seem to have. :?
[Pocket PC Thoughts]