FSK is described as second most used signaling format under which standard?

• A. UL
• B. ISO
• C. SIA
• D. NFPA

Answer: (C)

FSK, or Frequency Shift Keying, is a method used to transmit alarm events from the control panel to a monitoring station, often over telephone lines. In the alarm industry, the standards that describe and rank the signaling formats are maintained by the Security Industry Association. Within that framework, FSK is noted as the second most commonly used signaling format, reflecting its longstanding role as a reliable digital signaling method alongside the leading format defined by the same standard. The other organizations—UL, NFPA, and ISO—serve different purposes (product safety certification, fire and life-safety codes, and international standardization, respectively) and do not specify the ranking of signaling formats. So the standard associated with FSK’s description is the SIA standard.