The Simplex 565‑831 Duct Detector PC Board is a critical component designed for integration into Simplex 4098-series duct smoke detector housings. This two-wire printed circuit board enables precise smoke detection by continually sampling air within HVAC duct systems, delivering early warning of potential fire hazards in commercial and industrial environments. It features high-performance detection electronics built to differentiate smoke particulates reliably, while providing diagnostic readiness for maintenance and system verification . The board’s compact design ensures seamless fit inside standard OEM housings and simplifies installation or replacement . Suitable for spaces such as schools, hospitals, office buildings, and industrial facilities, the 565‑831 board plays a vital role in improving duct‑level fire monitoring and overall building safety infrastructure.