NAP-505 Series is the standard model of electrochemical carbon monoxide sensor that is newly developed and has high cost–efficiency. It is mainly used for civilian carbon monoxide detector and alarm. Its detection principle is the same with conventional ones, but NAP-505 adopts a new construction and thereby the risk of electrolyte leakage is reduced to almost “zero” level, and its small size has greatly reduced the production costs. NAP-505 has achieved UL2034 certification and won the favor from the majority of customers.