The ESL 511C two-wire, photoelectric, self-diagnostic smoke detector is a conventional direct-wire smoke detector with drift compensation. The 511C continually monitors its own sensitivity and operational status, and provides a visual indication if it drifts out of the sensitivity range or fails internal diagnostics. This meets NFPA 72 field sensitivity testing requirements without the need for external meters. Time between cleaning detectors is dramatically increased because of the 511Cs 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 the life of the detector. And when the 511C needs cleaning, its literally a snap with ESLs patented field replaceable optical chamber.