The SD Series photoelectric smoke detectors are engineered to meet strict UL fire safety codes and effectively respond to a wide spectrum of fires. The SD Series smoke detectors are suitable for use in commercial, industrial, institutional and residential occupancies. The sleek low-profile design of the detectors emphasizes ease of installation and field maintenance. The SD Series consists of six models: SD-2WP / SD-2WT / SW-2WP-LED / SD-2WT-LED The SD-2WP is a two-wire photoelectric smoke detector for use with electrically compatible fire alarm control units. The SD-2WT is a two-wire smoke detector that uses photoelectric technology in conjunction with a fixed temperature heat sensor to further extend its sensing capabilities. Additional two wire models (SD-2WP-LED and SD-2WT-LED) are available with a remote LED output. SD-4WP / SD-4WT The SD-4WP is a four-wire photoelectric smoke detector. The SD-4WT is a four-wire photoelectric smoke detector with a fixed temperature heat sensor.