Automatic heat detector with a single thermistor to sense the air temperature around the detector. Fast semiconductor sensor guarantees reliable detection of fires with rapidly rising temperatures and integrated fixed temperature function for the detection of fires with slowly rising temperatures. Ideal for sensing in environments that are dirty or smoky under normal conditions, as well it is unaffected by wind or atmospheric pressure. Intelligent fire detector with decentralized intelligence, automatic function self-test, CPU failure mode, alarm and operating data memory, alarm indicator, soft-addressing and operating indication. The detector is provided with an integrated isolator. A remote indicator can be connected.