According to NFPA 72, National Fire Alarm and Signaling Code, system smoke detectors must be functionally tested annually. This test involves introducing smoke or an approved smoke substitute into the sensing chamber to verify that the detector initiates an alarm signal at the fire alarm control unit. This ensures the detector's operational integrity and its ability to respond to a fire condition as designed. The annual frequency balances the need for reliable operation with the practicalities of building maintenance.

A. Monthly: This frequency is generally associated with visual inspections of control equipment (e.g., checking LEDs), not functional testing of individual smoke detectors.

B. Quarterly: This testing frequency applies to other system components, such as lead-acid batteries and certain supervising station communications equipment, but not smoke detectors.

C. Semiannually: This is the required testing frequency for components like supervising station alarm system transmitters and engine-driven generators, not system smoke detectors.

1. NFPA 72, National Fire Alarm and Signaling Code (2022 Edition). Chapter 14, Inspection, Testing, and Maintenance. Table 14.4.3.2, "Testing Frequencies," Item 17(g)(1). This table explicitly lists the test frequency for "System smoke detectors" as "Annually."

2. SFPE, Handbook of Fire Protection Engineering (5th Edition). Chapter 55, "Inspection, Testing, and Maintenance of Fire Protection Systems," Section 55.5.1, Fire Detection and Alarm Systems. This section references NFPA 72 and states, "Functional tests of smoke detectors are required annually." (DOI: https://doi.org/10.1007/978-1-4939-2562-455)

3. Oklahoma State University, Fire Protection & Safety Engineering Technology. FSE 3233 Fire Alarm & Detection Systems Course Materials. "Module 6: Inspection, Testing, and Maintenance." The courseware directly cites NFPA 72, Table 14.4.3.2, to establish that the functional testing of smoke detectors is performed on an annual basis.