System Sensor D4120 4-Wire Photoelectric Low-Flow Duct Smoke Detector provides reliable smoke detection in HVAC duct applications with wide operating ranges and advanced false alarm immunity. Its pivoting housing and plug-in sensor design simplify installation, testing, and maintenance across square, rectangular, and round duct systems.

• 4-wire photoelectric duct smoke detector with integrated low-flow sensing technology for HVAC systems
• Supports wide environmental conditions including airflow from 100 to 4,000 FPM, temperatures from –4°F to 158°F, and up to 95% humidity (non-condensing)
• Plug-in sensor head improves false alarm resistance while simplifying installation and maintenance
• Flexible mounting design fits square, rectangular, and round ductwork configurations
• Includes easy-access test/reset button, improved LED status indicators, and tool-free sampling tube installation