Siemens FDT421


Thermal (Heat) Detector

Availability: Estimated 6 - 8 Business Days

  • Factory New
Brand: Siemens Part #: 55106 Categories: , , Manufacturer Part #: FDT421Secondary Part #: S54320-F5-A1


The Intelligent Thermal (Heat) Detector (Model FDT421) provides an advanced method of detection, address programming supervision ─ combined with sophisticated FACP communication. Model FDT421 uses a state-of-the-art thermistor, microprocessor and advanced signal analysis, providing high reliability and accuracy.


Weight 0.40 lbs
Dimensions 1.93 × 4.13 × 4.13 in

Thermal Rating



Detection Method

, ,



  • Built-in ISOtechnology
  • Compatible with Siemens Model `H’- series devices on the same loop (with Desigo Fire Safety Modular | FireFinder XLS/V | FC/FV20–series fire-alarm control panels
  • Contains seven (7) field-selectable settings in a temperature range of 135°F – 174°F (57.2°C – 78.9°C)
  • Provides a low-temperature warning of 40°F (4.4°C)
  • Field programmable as rate-of-rise or fixed temperature
  • Tri-color detector-status light-emitting diode (LED) with 360° view
  • Compatible with Model DPU (device programmer / loop tester)
  • Utilizes advanced, microprocessor-based signal processing
  • Each detector is self-testing:
    • complete diagnostics performed every 10 seconds
  • Polarity insensitive via SureWire technology
  • Functions with Model DB-11–series mounting bases
  • Superior electromagnetic interference (EMI) and radio-frequency interference (RFI) immunity
  • Restriction of Hazardous Substances (RoHS compliant)
  • UL 521 Listed, ULC Listed; FM (#3230, #3210), CSFM (#7272-0067:0258) Approved


Thermal (Heat) Detector; Model FDT421
Siemens – Data Sheet
Model FDT421; Heat Detector
Siemens – Installation Instructions

Related Products...