What characteristic is unique to detector meters used in fire service?

Detector meters used in the fire service are designed with the unique capability to measure low flows when not in use. This feature is crucial in fire protection systems, as it allows for the detection of small water flows that might indicate issues such as leaks or unauthorized usage of water from a fire protection system. These meters are particularly sensitive to low flow rates, ensuring that even minor changes in flow can be monitored.

This characteristic helps ensure the integrity of the fire service system and assists in maintaining compliance with safety regulations. By being able to detect low flows, detector meters can alert operators to potential problems before they escalate, contributing to overall system reliability and safety.

The other characteristics, such as measuring high flow rates only or being the smallest type of fire meter, do not accurately describe the unique functionality of detector meters. Additionally, the inability to detect pressure changes does not apply to the design of these meters, as they are able to function under various pressure conditions while focusing on flow measurement.