System Sensor-4WTR-B Smoke,Thermal Detector

System Sensor i3 Photo Detector, Plug-In, 4-Wire, 12/24 Vdc, 135 ?F Thermal, Form-C Relay.4-wire photoelectric smoke detectors. All models incorporate a state-of-the-art optical sensing chamber and an advanced microprocessor. The microprocessor allows the detector to automatically adjust its sensitivity back to the factory setting when it becomes more sensitive due to contaminants settling in its chamber. In order for this feature to work properly, the chamber must never be opened while power is applied to the smoke detector. This includes cleaning, maintenance or screen replacement. All models also feature a restorable, built-in, fixed temperature (135?F) thermal detector and are also capable of sensing a freeze condition if the temperature is below 41?F