CorrSen records electrical resistance of a thin metallic track deposited on a non-conductive substrate and exposed under corrosive conditions. As a result of corrosion, the sensor thickness decreases leading to the electrical resistance increase. It is directly recalculated to the corrosion depth, actual corrosion rate and environmental corrosivity. Owing to the simple operation principle, the device is easy to maintain and provides direct corrosion data in all types of atmospheres. Simultaneously with the corrosion rate, temperature and relative humidity are recorded helping to understand observed changes in the environmental corrosivity.