The iAdaptAir has a built-in particle sensor. A green happy face indicates a low particle count or good air quality, the orange face indicates moderate air quality and the red frowning face indicates poor air quality. If your unit is always showing red, this could be a false response. It's usually caused by an excess build up of debris within the sensor. Use a can of compressed air gently blow any debris out of the sensor and the indicator should begin to operate correctly again. The array of small holes just the right of the indicator lights is where the sensor is located.