The 55000-139IMC from the Context Plus Series 65A is a conventional dual-mode heat detector (fixed-temperature + rate-of-rise) rated at 135°F (approximately 57°C). It is UL Listed and includes a flashing LED indicator to show normal standby status and alarm state. The detector is intended for use in environments where smoke detectors are unsuitable (e.g. dusty, smoky, humid areas). It uses a pair of matched thermistors (dual thermistor network) to monitor ambient temperature and rate of temperature increase, combining both signals to decide when to alarm. Key Features: Dual sensing (Fixed + Rate-of-Rise) — triggers if temperature rises rapidly or if fixed threshold of 135°F is exceeded; Flashing LED indicator — visible status signaling: flashes in standby, red solid in alarm; Wide supply voltage — operates over 9V to 33V DC, accommodating a wide range of conventional fire circuits; Low quiescent current — minimal current draw in standby (around 50 µA) to preserve power on wiring loops; Alarm current — ~52 mA at 24 V when in alarm condition; Ambient rating — 32°F to 100°F (0°C to ~38°C) typical for detection zones; Remote output — supports a remote LED indicator (sink current up to ~17 mA); Insensitive to wind / pressure changes — stable operation under airflow, making it reliable in variable HVAC environments; Standard mounting base compatibility — fits into typical Series 65A bases (e.g. 45681-200IMC); Robust design — flame-retardant polycarbonate housing, nickel-plated terminals. Industrial Uses / Applications: Mechanical / boiler rooms, engine rooms; Kitchens, utility rooms with dust, grease, or cooking vapours; Warehouses or storage with minimal smoke risk but heat generation; Utility corridors, areas where smoke detectors may produce false alarms; Environments with poor visibility or particulate matter.