Smoke Detector Photoelectric Four-Wire. The detector model is UL listed and works with commercial fire protective signaling and household fire warning systems. The model detects smoke particles produced during wood, paper, and fabric combustion. This detector uses an infrared (IR) LED light source and a silicon photodiode to measure light in a chamber. A fine screen covers the chamber to deter insects and reduce dust accumulation and nuisance alarms. During a fire, smoke particles reflect light onto the photodiode. When the photodiode measurements exceed the alarm threshold, the detector signals an alarm condition. After the alarm condition clears, interrupt power at the control panel to reset the detector.