When electronic equipment is used in harsh environments with long expected lifetimethere is a need to understand that environment more in detail. This situationis today a reality for many application areas including the automotive sector,heavy industry, the defense sector and more.To fully understand the working environment a unit has been developed to monitorphysical data such as temperature, vibration, humidity, condensation etc. to beused in the product development phase for new products.The paper presents the underlying principles for the ESU (Environmental SupervisionUnit) and details on the design.