Indoor Air Quality monitors come in different forms - some sit on your counter or table, some have a battery and can be carried around, while others are mounted to the wall. Most have the ability to measure the amount of particles and chemicals at varying degrees of accuracy and repeatability, though some devices are equipped with specialized sensors for certain gases or radon.

One thing these Indoor Air Quality monitors have in common is that they measure air only in the room where they are currently placed. Portable monitors can be moved from room to room, but can never measure all rooms at once. Most stationary or portable monitors also measure particles using the same technique: a small fan that forces the air through a laser beam. This method works well, but these small fans have mechanical parts that can fail if the device is dropped, if the motor or bearing fails, or if too many large particles clog the tiny air channel. To summarize: common air quality monitors only measure one room at a time, and have moving parts that can fail after a few years of use.

Most modern single family homes have a central air system that is designed to move the air throughout the whole home, while heating or cooling. Generally speaking, a home's air is circulated by the central HVAC system first through the return ductwork, then into the filter, air handler, and back out to the home via the supply ductwork. So why monitor the air in only one room, if there is a location that all of a home's air is being moved through?