The Telaire SM-PWM-01C SMART dust sensor detects the dust particle concentration in the air by using optical sensing methods. An infrared light emitting diode (IR LED) and a photosensor are optically arranged in the device. The photosensor detects the reflected IR LED light by dust particles in the air. The SMART dust sensor can detect small particles like cigarette smoke, and it can distinguish small particles such as smoke from large house dust by the pulse pattern of the signal output.