This 4 in 1 multi functions air quality meter is capable of measuring the Formaldehyde (HCHO), Total volatile organic compounds (TVOC), air temperature and relative humidity. It adopts the import high speed processor with quality sensing elements to provide precise & reliable readouts. The meter also equips with in-built rechargeable battery for long lasting run & back support stand for permanent locating. Four (4) levels of 'Smile face' indicator on the display are to present the condition of air quality in accordance to the level of measurements, along with high frequency audible alarm. It certainly provides a good indication of how healthy of your environment you are living in.