Sensitive Fire Alarm Circuit using Infrared IR LED

The Simple and inexpensive fire alarm circuit is highly sensitive. This Fire Alarm circuit alert through buzzer sound whenever any kind of fire detected in the air or an environment. It can detect any kind of fire such as radiation, heat etc. Depending on types a sensor that matches an application is selected. In the market, most of the circuits are expensive and difficult to buy. An Infrared Light sensor, on the contrary, is sensitive and very easy to use.

Components Required

The list of necessary components items required for Fire Alarm Circuit:

  • Infrared IR LED
  • LED for Indication any color
  • Transistor c945 or any npn
  • Buzzer
  • 3.7V Battery
  • Breadboard if needed
  • some peace of wires for connections

Working Explanation

An IR sensor is an electronics device that is used to detect infrared radiation falling on it. The heart of  fire alarm circuit is an infrared receiver and infrared transmitter. In default operating conditions when infrared light is shining from the infrared transmitter it will have low impedance. So the voltage at the base will be very low and the transistor will remain in off position. In case when a fire is detected by the infrared beam will not be able to pass to a receiver. The resistance of the receiver rises and the voltage at the base will become positive and transistor turn on. Buzzer and LED is connected with transistor will also be on.


  • Industries
  • Hospitals
  • Banks
  • Homes
  • Security departments

Circuit Diagram

Fire Alarm Circuit using transistor


Fir Alarm circuit for 9v

You can operate this circuit by suing 9 to 12v battery with slight change in the circuit. We have to use only 1 resistor with LED because LED will burn without resistor if we use more than 6 volts.

Sensitive Fire Alarm circuit

Fire alarm circuit can also be designed by using ic but the simple circuit according to my point of view is enough.

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