DF 303 - HD analogue addressable heat detectors are microprocessor controlled state-of-the-art analogue addressable detectors suitable for connection to addressable fire detection control and indicating equipment. Up to 254 detectors can be connected to each alarm zone loop. An electronic thermistor sensor provides sensitive rate-ofrise alarm operation, or fixed-temperature operation when the response threshold value is exceeded. The DF 303 - HD range of analogue addressable detectors provides fire detection and alarm system designers with a Standards-compliant, premium heat detector for property protection applications1 where smoke or multi-sensor detectors may not suitable due to environmental conditions.