A low-cost, low power consumption indoor environment monitoring instrument, called SKOMOBO (school monitoring box), was developed and tested. SKOMOBO includes sensors to monitor temperature/relative humidity, carbon dioxide (CO2), particulate matter and motions. SKOMOBO was developed using the open source hardware Arduino Pro Mini. This paper describes the process of building SKOMOBO, including sensor selection, printed circuit board design, sensor programming and performance evaluation. Two co-located tests have been undertaken; one in the controlled environment and one in the uncontrolled environment. Results show SKOMOBO measurements have high correlations with their commercial equivalents. In the two different testing environments, the R2 of temperature measurements for all six SKOMOBOs were 1. The R2 for relative humidity and CO2 measurements were above 0.9. The result of this work shows the reliability of SKOMOBO on monitoring indoor air quality.