Being aware and cautious are some of the synonyms for the phrase "be careful of". They imply being mindful of potential dangers that may lie ahead. "Watch out for", "be mindful of", and "be cautious of" are other synonyms that suggest being vigilant in the face of danger. Furthermore, "be on guard of" or "be wary of" propose being suspicious of any possible threats and being prepared for them. "Be attentive to", "be observant of", and "be vigilant of" communicate the importance of paying close attention to one's surroundings to avoid any potential risks. Ultimately, using these synonyms for "be careful of" can help individuals be more alert and ready to respond to any perceived dangers.