The term "safety chain" denotes a security device that prevents accidents, damages, or loss. Its opposite, or antonym, would be a term that signifies danger, risk, vulnerability, or instability. Potential antonyms could be things like "unsecured," "unprotected," "risky," "perilous," "hazardous," or "precarious." These words all suggest that without a safety chain or similar safety measures, something is left open to harm or threat. Depending on the context in which the term "safety chain" is used, antonyms could be used to describe situations that lack safety or security measures such as helmets for bikers or seat belts in a car.