Salwico EVC-PY-IS Intrinsically Safe Optical Smoke Detector N1144 The Salwico EVC-PY-IS N1144 is an intrinsically safe Evolution conventional optical smoke detector developed for explosion hazardous areas. EVC-PY-IS is connected to the fire alarm system via an intrinsically safe interface. Using the latest smoke sensing chambers, with enhanced sensitivity to black smoke. The EVC-PY-IS N1144 detector design provides strong immunity to air velocities, contamination and RF interference.