This paper presents a novel low-cost & multi-gas non-dispersive infrared (NDIR) gas sensing platform with sub-ppm detection capabilities, targeting environmental monitoring of greenhouse gases. The design of the NDIR sensor combines highest-compactness and low-power consumption, with a unique multi-channel optical cell design, featuring the detection of up to three different gases, simultaneously. Our flexible sensor platform allows a customer specific selection of the target gases, making the sensor adaptable towards a variety gas monitoring scenarios. We verify our concept by the detection of multiple selective gases, such as CO 2 , CH 4 and H 2 O. The embedded calibration model includes temperature stabilization and addresses in real-time any cross-sensitivity between the NDIR gas sensing channels. This novel versatile platform offers both, high stability, and high precision (