The Photoelectric | Thermal (Heat) Detector (Model FDOT421) is an intelligent, addressable multi-criteria detector that incorporates optical and thermal sensors, and uses signals in a neural network to create an intelligent multi-criteria detector. The encompassing result is a detector that provides enhanced detection to a wide range of products of combustion. Model FDOT21 is UL 268 7th Ed. listed and incorporates advanced built-in ISOtechnologyTM – True Class-X SLC operation (use is optional) greatly improves reliability, circuit integrity and provides advanced addressable fault finding. The multi-criteria detector additionally has state-of-the-art microprocessor circuitry (with error check), as well as detector self-diagnostics and supervision programs that is used on Desigo Fire Safety Modular | FireFinder XLS/V and on Model FC/FV20-series Desigo Fire Safety fire-alarm control panels (FACPs). Additionally, Model FDOT421 is a plug-in and addressable two-wire multi-criteria detector (with both photoelectric and thermal sensors) whose value is increased with built-in ISOtechnology feature, that is compatible with all current Siemens intelligent, addressable systems.