Models 5251B, 5251RB, and 5251H are intelligent sensors that utilize a state-of-the-art thermistor sensing circuit for fast response. These sensors are designed to provide open area protection with 50-foot spacing capability as approved by UL 521. Model 5251B is a fixed-temperature sensor with a 135°F fixed temperature alarm. Model 5251RB is a rate-of-rise temperature sensor with a 135°F fixed temperature alarm. Model 5251H is a high-temperature sensor with a 190°F fixed temperature alarm.

Two LEDs on each sensor light to provide 360° visibility of the sensor indication. The LEDs can be latched ON by code command from the panel for an alarm indication. The LEDs can also be unlatched to the normal condition by code command. Remote LED annunciator capability is available as an optional accessory (Part No. RA400Z/RA100Z).