Check the listing for details. System Sensor 5623 - Fixed Temperature Heat Detector 135°F. Condition: New. Listed at 32.99 USD. The System Sensor 5623 is a fixed temperature heat detector designed for reliable fire detection with a factory-set activation point of 135°F (57°C). Featuring a low-profile white housing and a durable thermal sensor, it provides accurate and consistent heat detection ideal for residential, commercial, and industrial applications. The 5623 uses a fixed temperature element that triggers the alarm once the set point is reached, ensuring fast response in high-heat scenarios where smoke detection may be insufficient. Compatible with most conventional fire alarm systems, it is UL listed, easy to install, and built for long-term performance. Its unobtrusive design blends seamlessly with interior environments, while the integral mounting bracket offers secure installation. Ideal for areas like.