D4240 photoelectric duct smoke detectors are 4-wire detectors that feature pivoting housings that fit both square and rectangular footprints and mount to round or rectangular ductwork. They operate in airflow speeds of 100 to 4,000 Feet/Minute, in temperatures of -4 to 158 deg F, and a humidity range of 0 to 95 percentage (non-condensing). Their plug-in sensor heads offer improved false-alarm immunity and simple installation, testing, and maintenance. An improved cover design isolates the sensor head from the low-flow feature for simple maintenance. The InnovairFlex housings provide ample wiring space, 3/4 Inch conduit knockouts, and built-in short-circuit protection to prevent damage to sensitive components during installation. High-contrast terminal designations make wiring easy. With its 2:1 sensor-to-power capability, the power board of the D4240 may be used to monitor a second sensor, D4S, simultaneously (i.e., supply and return side). As many as 50 InnovairFlex detectors can be interconnected. When one unit senses smoke, all interconnected detectors will switch their relays; only the detector sensing smoke will go into alarm, enabling the fire location to be pinpointed.