fire alarm circuit | fire alarm

There are Millions of fire alarm circuit available on the internet but the circuit shown below is probably the easiest for beginners to follow.

We are already aware of the importance of fire alarm and it’s presence in the crowded or public places.

So, presenting fire alarm as your project can be reasonable and it would be easy to explain it too. There is so much to say about its application.

The Speciality of my design is –

  1. Easy / simple circuit
  2. Low cost

Components required

  1. IR receiver
  2. LED ( red )
  3. Transistor BC548
  4. Resistor 100 Ohm 0.25W
  5. Small buzzer
  6. Switch
  7. Connecting wires
  8. 4v – 6v power supply ( battery )
  9. Vero board / Breadboard

bc548 Pinout

The pin configuration of BC 548 transistor is shown in the diagram below

bc 548 Pinout

fire alarm circuit

The circuit diagram for the fire alarm is shown below

Fire alarm circuit


Make your connections step by step as mentioned below

  1. Take BC548 transistor and connect IR Receiver to its base pin as shown in circuit diagram.
  2. Connect one terminal of buzzer to collector pin of transistor and the other terminal to positive source through switch.
  3. Make a series combination of red led and 10 Ohm resistor and connect it in parallel to buzzer.
  4. Add switch as shown in circuit.
  5. Connect the emitter pin of transistor to negative terminal of power source.
  6. Connect the power source and switch it on.

Working of fire alarm circuit

On this circuit the IR receiver is a sensor and when it is connected to base pin of transistor the combination ( sensor and transistor ) acts as switch.

Fire contains infrared rays. These infrared rays when fall on IR receiver it conducts a small current from positive terminal to base.

This small current to base allows the flow of current from collector to emitter. The flow of current through transistor completes the circuit of buzzer and led and makes them beep / glow.


The following precautions should be taken –

  1. Handle fire carefully. Make sure you make small fire using matchstick or lighter to demonstrate your project.
  2. Make connections according to the circuit diagram. Semiconductor devices like diodes and transistors are very sensitive.


Akash Sharma

Discover more –

  1. LDR Circuit
  2. Piano Circuit Using 555IC

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