Antonyms for "puts on guard" would be words or phrases that represent a lack of vigilance or alertness. These could include "lets their guard down," "ignores potential threats," or "relaxes their defenses." Other antonyms might be more specific, such as "invites danger," "welcomes their enemy," or "embraces risk." Essentially, any language that suggests a lack of protection or a failure to recognize potential threats could be considered an antonym for "puts on guard." In contrast, synonyms might include phrases like "heightens caution," "raises awareness," or "bolsters defenses.