Not that difficult. Take a look at
http://wiki.maemo.org/Documentation/...larm_Framework
and
http://maemo.org/api_refs/5.0/5.0-fi...balarm_8h.html
especially alarmeventflags
http://maemo.org/api_refs/5.0/5.0-fi...0a1c372999f681
CepiPerez used a flag called ALARM_EVENT_BOOT
But it seems this does not work as expected, it does
not show the alarm ui.
The builtin worldclock application uses the flag
ALARM_EVENT_ACTDEAD
That way, the alarm event boots up the device to acting dead mode
and shows the alarm ui. After you hit the "stop" button it asks for
booting the device.

You can compare the "flags:" property in /var/cache/alarmd/alarm_queue.ini for entries from
your worldclock application with the one
created by the builtin clock application.