A handheld indoor air-quality data logger that tracks up to three plug-in probes at once, covering CO, CO2, O2, temperature, humidity, dew point and wet-bulb readings on a backlit dual LCD. Logged data writes straight to a removable SD card (expandable to 16GB) at sampling intervals from 1 second to 8 hours, so long unattended monitoring runs can be exported later as a spreadsheet without extra software. Well suited to checking ventilation and CO2 buildup in schools, offices, and hospitals, with Max/Min and data-hold functions for spot checks. Ships as a kit with the humidity, CO, CO2 and O2 probes, carrying case and batteries.