An alarm system stands for vigilance, the part of you that watches for danger. Dream books read a false alarm as anxiety running ahead of reality, and a silent one as feeling unprotected.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.