The antonyms for the phrase "are on guard" include relaxed, carefree, unworried, and unguarded. They describe a state of being where one is not watchful or cautious, and is not anticipating any potential dangers or threats. A relaxed and carefree person may be less vigilant about their surroundings and the risks that exist in their environment, while an unguarded person may leave themselves vulnerable and unprotected from possible harm. In contrast to being on guard, these antonyms portray a more carefree and casual attitude towards one's safety and wellbeing, which can sometimes lead to dangerous consequences.