The ESL 449/448 Series self-diagnostic, four-wire smoke detectors continually monitor their own sensitivity and operational status, and provide a visual trouble indication if they drift out of sensitivity range or fail internal diagnostics. This unique, patented technology 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 if service is required.This series is easily cleaned by simply replacing ESL's proprietary field-replaceable optical chamber. All models are designed to reduce false alarms from dust, insects, RFI, and external light. An integral combination rate-of-rise and fixed 135 degrees Farenheit (57 degrees Celsius), 50-footrated, heat sensor is available with all ''T'' model detectors (see selection guide), allowing latching of the alarm for either smoke or heat. The 449CSRH includes an isolated alarm. GE Interlogix.