The NOTIFIER® FST-951 Series consists of addressable, plug-in thermal detectors engineered as drop-in replacements for the legacy FST-851 Series. Utilizing advanced thermistor technology housed in a modernized enclosure, these devices provide reliable property protection while satisfying aesthetic architectural demands. Signaling Line Circuit (SLC) addressing is established via integrated rotary decimal dials, ensuring explicit point identification at the control panel. The series comprises three distinct models: 135°F (57°C) fixed-temperature, 135°F (57°C) rate-of-rise, and 190°F (88°C) high-temperature units. Depending on system specifications, these detectors can be deployed on either FlashScan® or CLIP polling loops.