Post-occupancy monitoring of building performance is still not commonplace within the commercial building sector in the United States. As building owners strive to reduce operating costs further, an increased interest in post-occupancy measurement and verification has developed. Measurement and verification can only be successful with the availability of low-cost, but reliable tools. Onset Computer Corporation has long been one of the leading suppliers of field deployed dataloggers and continues to develop units with increasing accuracy, at reasonable price points. Onset is now focusing on wireless technology, to allow download of data with greater ease. Users should look carefully at datalogger specifications to ensure sufficient accuracy, suitability to the environment being measured, and calibration requirements.