Through the interaction between a community security guard and a suspicious man, the boundary between duty and law was explored. The security guard discovered abnormal behavior of a man during night patrols, and through questioning and verifying information, found that the man was not a resident of the community. When the man attempted to leave, the security guard insisted on calling the police and preventing him from leaving to protect the safety of the community. After the police arrived, they confirmed through surveillance video that the security guard's behavior was reasonable, and ultimately decided to terminate the investigation into the man. This process demonstrates the vigilance and legal awareness of security personnel in fulfilling their duties, and also reflects that when dealing with suspicious situations, facts and laws should be the basis, rather than personal subjective judgments.