DF 502 - HD conventional heat detectors are state-of-the-art detectors suitable for connection to conventional fire detection control and indicating equipment, or to addressable fire detection control and indicating equipment that can accept conventional type detectors1. An electronic thermistor sensor provides sensitive rate-ofrise alarm operation, or fixed-temperature operation when the response threshold value is exceeded. The DF 502 - HD range of conventional detectors provides fire detection and alarm system designers with a Standards-compliant, economical heat detector for property protection applications2 where smoke or multi- sensor detectors may not suitable due to environmental conditions.