What type of fire alarm signal indicates that a fire detection system functioned correctly but required no response?

The most accurate choice for indicating that a fire detection system functioned correctly but required no response is "Unnecessary alarm." This term refers to a situation where the system has detected a condition that could suggest a potential fire, yet upon investigation, it turns out that there is no actual fire or need for response. This can occur due to various non-threatening conditions that mimic a fire event, such as steam or cooking smoke.

A true alarm would indicate that there is an actual fire or emergency requiring immediate action. Meanwhile, a false alarm signifies an incorrect activation of the system that does not relate to a real fire event. System fault describes a malfunction or issue within the detection system itself, which would not apply to a situation where the system worked correctly but did not require a response. Therefore, the term "Unnecessary alarm" properly conveys the idea that an alarm was triggered, but no action is needed because the situation does not warrant a response.