Open-eyed is an expression mostly used to describe a state of being alert or watchful, typically characterized by a sense of awareness and keen observation. There are numerous synonyms that could best describe this state of being. "Wide awake" and "alert" are two frequently used synonyms. "Vigilant," "observant," "attentive," and "watchful" can also be used as alternative expressions. "Perceptive," "sharp," and "wary" are other options that can be used in different contexts. Overall, when talking about someone being open-eyed, there are numerous synonyms that can be used to convey the meaning in various situations.