The ESL 500 Series self-diagnostic, 2 and 4-wire photoelectric smoke detectors are the industry's first conventional direct-wire smoke detectors with analog features such as drift compensation, multi-criteria detection and remote maintenance/trouble reporting (CleanMe®) on the 2-wire. The 500 Series continually monitor their own sensitivity and operational status, and provide a visual and remote trouble condition 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. The 521 has a unique feature enabling it to send a signal (CleanMe) to the ESL 505 module (sold separately) when it has drifted outside of its UL Listed sensitivity range or has failed its internal diagnostic test. The 505 is an interface module that will signal 24V panels via relays when the 2-wire 500s are dirty. Several control panels have the CleanMe software built in, eliminating the need for the 505 module. When CleanMe is not desired, simply leave the switch on the 2-wire series off and it will work as a normal 2-wire detector. CleanMe allows the installer time to schedule a service call and avoid a false alarm. Time between cleaning detectors is dramatically increased because of the 500s 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 500 Series has told you that cleaning is necessary, its literally a snap with ESL's patented field replaceable optical chamber. The multi-criteria model 500XT 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 sampling rate increases to detect smoke faster. Overview