The project Southern Wide-field Gamma-ray Observatory (SWGO) aims to build an array of air-shower detectors in the Southern hemisphere. Preliminary site searches identified suitable sites in Argentina, Bolivia, Chile and Peru. Site environment (including weather, seismic activity and also the electric field) is one of the key aspects to be considered in the site selection and should be based on reliable and comparable measurements.
We describe an environmental monitoring device to equip several candidate sites proposed for the SWGO. The individual monitoring sensors, control unit and the data storage together with the power system and data transfer concepts are specified. We also present the results of a long term cross-calibration campaign and a climate chamber evaluation of the proposed devices.