In recent years, we have developed an advanced environmental monitoring system (AEMS) containing an eco-sensor, meaning a sensor for the measurement of environmental pollutants, based on lipid membranes, for continuous monitoring of underground water in industrial areas such as semiconductor factories (Ishimori Y, Tamura H, Kawano K, Aoyama N and Tamiya E 2000 Proc. Photonic East 2000 pp 43-50). The AEMS project is made up of three components as follows: (1) the eco-sensor, (2) prediction of plume propagation using a computer simulation technique, and (3) the environmental protection method. In this paper, we would like to focus on the study of the eco-sensor. We considered modified lipid membranes to serve as good models for cell membranes because they would be ideal hosts for receptor molecules of biological origin or disruptive environmental pollutants. Thus, we selected the lipid membrane as an environmental sensing element. In attempting to improve the applicability and the responsivity of bilayer lipid membranes (BLMs) in the eco-sensor, we have investigated automatic BLM preparation devices. An automatic BLM preparation device was made by use of an inkjet mechanism. The reproducibility of the BLM preparation was remarkably improved. The sensitivity to volatile organic chlorinated compounds such as cis-1, 2-dichloroethylene was of the order of 10 ppb using mono-olein BLMs even in real underground water. We have also been developing a smaller eco-sensor for practical use.