This is a steam sensor which is can sense a rain drops, steam or water vapor suitable of IOT project. The illustration below use LM3XX as differential comparators that drives the difference between the two inputs. The LM3XX device is
Wiring SenseAir LP8/S8 IR CO2 Sensor on TI CC3200 IOT-MCU
SenseAir Miniature (Carbon Dioxide) CO2 Sensor are non-dispersive small package infrared (NDIR) sensor, a new optical design that enable a precise and accurately measures carbon dioxide level up to 5% that runs on 30mA design for long-term battery or solar