I never even use an alarm. I use a mantra like "I will wake up and remember it all" when I first go to bed, and I wake up usually around 3:00 AM, usually with something recalled. I give it a few minutes to make sure I've recalled everything I can, but I don't write it down just yet; that's a task I save for the morning, since once I've clearly recalled a dream I can remember most of the details on demand, even after going back to sleep. I managed to pull off my first willing LD, a DEILD, like this; I've never used an alarm for any of my LD attempts.