135° Fixed Temp/Rate-of-Rise Heat Detector, Single Circuit. The 104 Series detectors offer rate-of-rise/fixed temperature and fixed temperature only features for high performance and reliability. The rate-of-rise feature detects intense fires by responding to rapid temperature increases. The fixed temperature f eature reacts to fires when a specific temperature is reached. Materials for the 104 Series heat detector are carefully selected for strength, corrosion, resistance, and integrity at points of hermetic sealing. The detectors require normal periodic tes ting and no field maintenance. The low silhouette and white finish blend with most ceiling designs to make the detector unobtrusive.