Santacary HCHO Index Monitor, Formaldehyde (Oxymethylene) Temperature and Humidity Air Quality Pocket Indicator [FH20] Accurate AQI Datalogger Indoor Detector *Two-year Warranty* FH20 detects low level concentrations of hazardous formaldehyde vapors with a resolution of 0.01 ppm Electrochemical sensor for formaldehyde detection Trend display available for easy understanding about formaldehyde change in up to 8 days FH20 should be the smallest and the lightest formaldehyde monitor in the world FH20 can also measure the ambient temperature and the relative humidity; Selectable C and F