Which statement is true regarding elevator recall smoke detectors?

Elevator recall smoke detectors play a crucial role in ensuring safety during a fire emergency by facilitating the safe operation of elevators. The correct statement emphasizes that these detectors must be integrated into the building's fire alarm system. This requirement is essential because it allows the fire alarm system to coordinate with the smoke detectors, ensuring that elevators are recalled to a designated safe floor when smoke is detected in the vicinity of the elevator lobbies or shaft. This integration prevents elevators from malfunctioning or stopping in unsafe areas during a fire, ultimately protecting occupants and first responders.

Being part of the building's fire alarm system allows for centralized monitoring and control, ensuring that all safety measures work in concert. The other options suggest conditions that would not meet necessary safety standards. For instance, smoke detectors that are not part of the fire alarm system would lack the necessary communication with other alarms and emergency systems, compromising occupant safety.