The phrase "be alarmed" implies a sense of apprehension or concern. There are many synonyms that can be used in its place, depending on the context and degree of urgency. Words like "concerned," "anxious," "distressed," or "worried" can be used to convey a sense of unease. Alternatively, more urgent synonyms like "frightened," "panicked," "terrified," or "horrified" may be used to indicate a more pressing danger. Less intense synonyms like "alert," "cautious," or "vigilant" may also convey a sense of heightened awareness without necessarily implying extreme danger. The choice of synonym will depend on the context and intended meaning of the message.