Aim of the Closed Habitat Environmental Control Sensors (CHECS) project has been the setting up of a complete, lightweight sensing system for monitoring the ambient conditions of plant growth in space missions. A complete sensor system has been developed and tested, based on a deep knowledge of plant needs, and on the typical plant behaviour in stress conditions.The main characteristic of the system is its compatibility with Silicon technology. This means high integrability, reduced dimensions, low weight, redundancy, simplicity and high reliability. All the sensors composing the systems have been produced by means of well developed solid state technology, including the MicroSystem Technology (MST) and Porous Silicon Technology (PST). The latter has proved in the last year to have considerable advantages over other approaches.The first main feature of the use of Porous Silicon Technology is the high sensitivity to gaseous species with reduced concentration, which are chemisorbed or physisorbed on the huge internal surface of the Porous Silicon network, giving rise to an electrical signal, to be processed by the control electronics [1, 2 and 3]. A second feature is the tunability of the basic optical properties of Porous Silicon, depending on porosity, which allow for the production of high quality optical devices, directly integrated onto a Si chip [4, 5 and 6]. The third feature is the possibility of impregnating, or oxidising the porous skeleton, in order to maximise the response for desired species, or to minimise it for interfering agents. The high level of integrability of the sensor onto a Si chip is the fourth, important feature, together with the possibility of applying large-scale integration techniques. A further consequence is the possibility of sensors redundancy.With these features, a PST humidity sensor, a VOC Pattern detector based on an array of thin film sensors, a PST colour sensor for monitoring the optical absorption of plant leaves and a PST selective sensor to CO2 have been designed, manufactured and tested in a dedicates plant growth chamber.