Low-cost devices are now offered commercially for monitoring indoor air quality (IAQ). Potential benefit exists in having data on IAQ parameters from more buildings, more locations in buildings and over time. For example, the spatial resolution that is possible with multiple sensors in a single office or residence providing empirical data could reveal the degree of uniformity of airborne contaminant concentration. With continuous logging, detailed temporal resolution can also be attained. Arrays of sensors can generate lots of data, but then the data need interpretation, and that should start with judging the quality of the data, which is currently not known for many of these sensors.