The Siemens FDCIO221 module is an essential component of Siemens fire detection systems, specifically from the Cerberus PRO series. This input/output (I/O) module allows the integration of external devices into the system, enabling signal monitoring and actuator control. This article provides a detailed technical overview of the FDCIO221 module, covering its features, technical specifications, operation of inputs and outputs, communication, installation, compliance standards, and practical applications.