Each unit develops directives for the operation and what aspect of the duress alarm system?

The correct choice is focused on the requirement that each unit must establish directives regarding the operational aspects of the duress alarm system, specifically related to its regular testing. This ensures that the system remains functional, reliable, and ready for use in an emergency. Regular testing helps to identify any faults or failures within the system, thereby maintaining a high level of operational readiness.

Quarterly testing typically implies a routine inspection and evaluation of system performance, which aligns with standard practices for security systems. Such testing not only checks that the alarm activates but may also involve verification of related response protocols, reinforcing the system's effectiveness in real situations where it may need to be used.

In contrast, while annual training, monthly inspections, and emergency procedures are all important components of effective safety and security protocols, they do not specifically address the operational checks required to ensure the duress alarm system itself is functioning as intended on a consistent basis. Thus, the focus on quarterly testing is crucial for maintaining the integrity and effectiveness of the alarm system over time.