Chemical warfare agents such as OPs and vesicants pose a serious threat to military personnel. These agents may be contaminating food or water or may be aerosolized and exist as a liquid to contaminate by penetrating skin. Thus, fast detection of CWAs in all of these forms is of paramount importance to prevent casualties. We previously reported that polyurethane-linked cholinesterases yielded a biosensor product with similar enzyme activity as soluble enzyme. We now report that an immobilized coupled choline oxidase-horseradish peroxidase biosensor exhibited remarkable stability suitable for detection of CEES/HD in water. The immobilized enzyme biosensor was more sensitive than the current HD detection kit, and additionally is environmentally friendly since mercuric cyanide is not a component of this immobilized biosensor. The coupled enzyme reaction provides not only rapid colorimetric and fluorometric indicators, but is easily adapted to miniaturized electrochemical techniques for CEES. The biosensor, due to its stability to harsh environmental conditions, can be incorporated into a variety of products. With the constant threat of chemical warfare or terrorist acts, the development of rapid, sensitive, lightweight, and stable personal biosensors is critical.