I recently purchased DreamZ, an app for the iPhone that maps your sleep cycles at night and provides audio cues in order to help you have a lucid dream. I tried using some of the built in audio cues in it with no success. If I played it too loud I would wake up and if it was too low nothing would happen. Now on most days, I wake up the the song Glorious Morning by Waterflame. So I decided to try using that song as a trigger sound. The result was that it actually worked, I became lucid during the dream. My guess is that your brain must somehow relate your everyday alarm sound to being awake and conscious so when it played I became lucid. You can download a Lite version of the app in case you want to try out this technique.