2.LCD display detecting CO2 level, as well as  temperature and relative humidity 3.NDIR infrared CO2 module inside with special ABC_Logic Self Calibration System. It makes the CO2 measurement more accurate and more reliable in use. 4.*5 years lifetime of CO2 sensor 5.Gentlest shape and convenient installation structure 6.Particular LCD display with three color (Green/Yellow/Red) backlights 7.Two alarm ways: buzzer alarm and backlight colours switch 8.Provide optional 1xrelay output to control a ventilator 9.Easy touch for operation *0.Provide four CO2 values to be preset to control the relay. *1.Optional RS**5 communication interface, *5 KV antistatic protection, individual IP address *2.Trusty quality with lower price