3 Review(s)

Fire alarm is device that gives indication of alarming sound with Light when fire took place near that device. In the circuit, an audio BUZZER is working as fire alarm. Transistor T1 working as SWITCH under Common Emitter configuration, whose output from collector is fed to the LED and Buzzer to give audio visual indication. When thermistor is being heated by match stick, the internal resistance drops to a certain extent. This makes transistor to conduct and that allows the current to flow from positive to negative through LED and buzzer in parallel.