Check the listing for details. System Sensor D4120 4 Wire Photoelectric Duct Smoke Detector. Condition: New. Listed at 150.00 USD. Get advanced smoke detection technology with the System Sensor D4120 4 wire photoelectric duct smoke detector. This device offers reliable smoke detection in commercial and industrial settings, ensuring your facility is safe from potential fires. Designed by System Sensor, a trusted brand in the industry, this smoke detector is made to last and perform at a high level.This smoke detector is specifically designed for use in HVAC systems and features a four-wire design for easy installation and maintenance. The Model D4120 is a photoelectric duct smoke detector that offers exceptional sensitivity to smoke and can help protect your facility in the event of a fire. Invest in the safety of your business or industrial space with the System Sensor D4120.