This paper describes a non-dispersive infra-red CO2 gas sensor, incorporating a midinfra-red solid state light source/ detector combination, tuned to match the spectral absorption characteristic of CO2 gas. Injection moulded optics provide low cost manufacture. Continuous operation power consumption is < 3.5mW and pulsed mode with energy per measurement < 6mJ. Self powered operation using a solar cell is demonstrated together with wireless capability. Performance of two path length variants (20mm and 70mm) is described. The sensor shows invariant temperature output characteristic from -25 to 50ºC. Accuracy level is typically ±3% of reading.