gas safety device 1)3 wire connection 2)Display:backlight LCD, LED ... 3)Unit:ppm, mA, %,%LEL,%VOL 4)Humidity:10-95%RH CO2 gas ... detector Technical features* 4-20mA, 3 wire connection ,compatible with existing alarm ... * Multi-parameter backlight LCD display: measuring range,digital gas reading ,units, bar graph , system status etc.* ...