The ET-4 Air Quality Sensor monitors indoor air quality, and instantly displays a reading of the value on a scale of 0 (good) to 500 (bad). This value is displayed on the LCD, along with a quick color code, to identify any dangers. The information is also transmitted to the EW-3 weather station, as an additional sensor. Thus, the air quality sensor can be used stand alone or with the EW-3.

Unlike other "air quality" meters on the market, the ET-4 is advanced and measures many different air borne particles, including pollen, dust, and other volatile air particles. This is then translated into an easy-to-read number and level.

Operates on AC adapter. Four "AA" batteries (not included) can be used for short term measuring and transmitting, but only last about five hours.