Formaldehyde TVOC and HCHO, planar semiconductor gas sensor, high sensitivity, 0~3.000mg/m⊃3;(HCHO) 0~9.999mg/m⊃3;(TVOC) range, 0~50° temperature, fast restored response time long operation life, 15%~90%RH operating humidity, 3-paremeter formal meter dire city measures airborne formaldehyde cocecentrations as well airborne TVOC and ambient temperature, appearance of light and novel, easy to carry, easy to operate, 3AAA / 7 alkaline batteries.