The more advanced systems are really trick. The iGS-110 controls temperature and humidity, the iGS-100 is for CO2 and the 220 does CO2, temp and humidity.  The also have a two box setup with the power box universal for all the systems, the controller boxes are all different. They connect with an eight wire ethernet cord that can be extended up to fifty feet if needed. All three have a built-in fan to circulate the air past the sensors for faster measurements. The 220 has a built-in clock and can log the high low and average levels over the past twenty-four hours so you can check how you system is working. It even includes a tips feature that will give you tips on how efficient your equipment is working. Noting for instance how long your exhaust fan is running and alerting you if it is running too long. Do you need a larger fan? The 220 also has an alarm feature that can be programmed for events like high temperature, this can then trigger the relay outputs for controlling a lighting relay or phone dialer.