Getting the Android’s AlarmClock application source from official repositories:
git clone git://android.git.kernel.org/platform/packages/apps/AlarmClock.git
To get the head version for an old platform like the 1.4 (codename donut), choose the correspondent branch using -o or –origin:
git clone git://android.git.kernel.org/platform/packages/apps/AlarmClock.git --origin donut