Extech FM100 Formaldehyde Monitor Adjustable audible alarm for readings exceeding set point (default at 0.08ppm) Visible bright tri-colored (green, yellow, red) LED alarm indicator Selectable CH2O unit as ppm or mg/m3 The Extech FM100 doesnt have a power on/off switch, this is similar to our other monitors (CO200, 220, 230) Kindly refer to the Technical details for Use Guide