The ESL 541 Series self-diagnostic, four-wire smoke detectors are the industry's first conventional direct-wire smoke detectors with analog features such as drift compensation and multi-criteria detection. The 541 Series continually monitor their own sensitivity and operational status, and provide a visual indication if they drift out of the sensitivity range or fail internal diagnostics. This meets NFPA 72 field sensitivity testing requirements without the need for external meters. Additional diagnostic information is activated by applying a magnet near the detector's integral reed switch. This initiates a self-diagnostic routine and provides visual indication of sensitivity level or indicates if service is required. Time between cleaning detectors is dramatically increased because of the 541's built-in drift compensation. This feature, usually only available in analog systems, allows the detector to automatically adjust its sensitivity over time as it becomes dirty, increasing dust life. And when the 541 indicates that cleaning is necessary, it's literally a snap with ESL's patented fieldreplaceable optical chamber. The SmartHeat™ model 541CXT photoelectric smoke detector/fixed rate of rise heat detector includes fast response algorithms for a quick response to both flaming and smoldering fires. Fast response algorithms allow the heat detectors to work intelligently together with the photoelectric smoke detector. As soon as the heat sensor detects a rapid rise in temperature, the sensitivity of the photoelectric sensor increases. This increase allows the sensor to detect smaller particles of combustion quicker.