AECL undertook the development of a software tool to assist alarm system designers and maintainers based on feedback from several utilities and design groups. The software application is called the CANDU Alarm Analysis Tool (CAAT) and is being developed to: Reduce by one half the effort required to initially implement and commission alarm system improvements; improve the operational relevance, consistency and accuracy of station alarm information; record the basis for alarm-related decisions; provide printed reports of the current alarm configuration; and, make day-to-day maintenance of the alarm database less tedious and more cost-effective. The CAAT assists users in accessing, sorting and recording relevant information, design rules, decisions, and provides reports in support of alarm system maintenance, analysis of design changes, or regulatory inquiry. The paper discusses the need for such a tool, outlines the application objectives and principles used to guide tool development, describes the how specific tool features support user design and maintenance tasks, and relates the lessons learned from early application experience. (author). 4 refs, 2 figs.