Fire Alarm Using Thermistor

This small and simple fire alarm circuit uses thermistor as the heat sensor. When temperature increases, its resistance decreases, and vice versa. At normal temperature, the resistance of the Thermistor (TH1) is approximately 10 kilo-ohms, which reduces to a few ohms as the temperature increases beyond 100 C. The circuit uses readily available components and can be easily constructed on any general-purpose PCB. You can used this circuit as Home-Security purpose.


Circuit Diagram:

Fire Alarm Circuit Diagram