Extech-CO210-Air-Meter-&-Data-Logger-EXTECH-CO210-The-Extech-CO210-air-meter-&-data-logger-checks-for-carbon-dioxide-CO-SUB-2-SUB-concentrations-using-a-maintenance-free-non-dispersive-infrared-NDIR-CO-SUB-2-SUB-sensor-This-neat-desktop-unit-displays-indoor-air-quality-in-ppm-with-Good-380-to-420ppm-Normal-lt-1000ppm-&-Poor-gt-1000ppm-indication-If-required-poor-air-quality-will-trigger-a-visible-&-audible-CO-SUB-2-SUB-warning-alarm-with-a-relay-output-to-activat