Simple Smoke Detector Alarm Circuit


BySaddam 19

Simple Smoke Detector Alarm Circuit

Smoke Detectors are very useful in detecting smoke or fire in buildings, and so are the important safety parameters. In this project, we are going to build a Simple Smoke Detector Circuit without using any Microcontroller. This circuit triggers the Buzzer whenever it detects Smoke or fire near by it. This circuit mainly uses MQ6 Smoke/Gas sensor to detect the level of smoke. MQ6 gas sensor is also sensible to LPG, Alcohol, and Methane etc. Here we have used Buzzer as a Smoke alarm, which is driven by BC547 NPN transistor.

We have previously built Smoke Detector Arduino Shield using MQ2 Gas Sensor, which not only sense the smoke in the air but also displays the level of Smoke in the Air in PPM.


Components Required:

  1. BC547
  2. Bread Board
  3. Smoke Sensor (MQ2/MQ6)
  4. 1K
  5. 10k POT
  6. Power Supply
  7. LED
  8. Buzzer
  9. Connecting wire
  10. Jumper wire

Smoke Sensor MQ6


Circuit Explanation:

Circuit Diagram of this Smoke Detector Project is given below:

Smoke detector alarm circuit diagram

In this circuit, we have used an MQ2/MQ6 Smoke Or Gas Sensor Module for detect smoke present in the air. A BC547 NPN transistor is used to to drive buzzer whenever it detects smoke. A 10K pot is also used for calibration. Basically, in this project, we have designed a Voltage Divider Circuit by using MQ6 smoke sensor (as resistor) and potentiometer. MQ6 has a resistance and its value changes whenever it senses smoke.


Working Explanation:  

Working of this Smoke Detector Alarm Circuit is easy. In this project, we have used transistor operating properties to work this circuit as a smoke detector. As we already know that we have used a BC547 NPN transistor which will turn on whenever it gets least 0.70v at its base terminal. So we have applied a Voltage Divider Circuit at its base.

Smoke detector alarm block diagram

Smoke detector alarm circuit with buzzer

But before using this circuit, we need to calibrate it by using pot. In calibration, we have applied voltage just below than 0.70v at transistor base. Whenever smoke sensor senses smoke, it reduces its resistance and due to this decrease in resistance, voltage across the base of the transistor increases. Now when the voltage at the base terminal of transistor become more than or equal to 0.70v then transistor turns on and LED lights up and buzzer also starts beeping. And when there is no Smoke, both the indication components turns off as the voltage across base terminal of transistor goes below the 0.70v. Check the Demonstration Video given below.

Also check our LPG Leakage Detector using Arduino.


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  • padmanahan's picture
    Nov 18, 2017

    1.which sensor has the higher level of sensitivity to kitchen burning smoke MQ2 or MQ6?

    2.Is this kit can be used for longtime domestic purpose or just for making projects?

    plz reply as soon as possible.

  • Aswinth Raj's picture
    Aswinth Raj
    Nov 21, 2017

    Both the sensors can be used.

    This kit is just a project you can use the same concept with some protective circuits to make it run for a long time as a prototype however it cannot be a consumer grade product 

  • Queenie's picture
    Dec 12, 2017

    How would I use an mq2 gas sensor with 4 pins, grnd, Do, Ao, Vcc? Where can I buy the sensor itself with no circuit?

  • SAURABH KESARI's picture
    Dec 25, 2017

    hello sir i have connected all components in same manner led is lowing whenever it is detecting gas but buzzer is not beeping .how to solve this problem??

  • AISHA's picture
    Dec 26, 2017

    In the circuit diagram the LED and buzzer are connected in parallel. If your LED is working but not the buzzer the problem could be

    1. You mis-matched the polarity of the Buzzer. Buzzers have polarity make sure if you have followed it correctly

    2. Try replacing your buzzer, the one in your circuit might not be working properly

    3. Check your connections  

  • Steve's picture
    Jan 24, 2018

    Has anyone measured the power consumption?
    How long would the 9V battery last?

  • Ryan's picture
    Feb 04, 2018

    How did you calibrate ng MQ-2 sensor? Or does it need to be calibrated first or is it good-to-go?

  • Bharath's picture
    Feb 10, 2018

    Pin connection

  • Abhishek 's picture
    Feb 25, 2018

    I have connected the MQ-6 sensor for detection of smoke to raspberry pi but the smoke of incense stick same as the video or any other is not detecting but detecting LPG gas.So please help me to solve it.

  • Aswinth Raj's picture
    Aswinth Raj
    Feb 26, 2018

    We can help only if you share your circuit and brief your problem 

  • Sachin's picture
    Apr 02, 2018

    I have connected in same manner as shown in diagram. I have used MQ 6 sensor but when we put smoke, nothing happen.
    Plz tell me what is reason behind it.
    Is required MQ-2 sensor for Smoke detection.

  • Jing's picture
    May 10, 2018

    Does MQ6 sensor also work on this circuit?? i have mq6 module, how do i connect?

  • Wayne Clinton 's picture
    Wayne Clinton
    May 27, 2018

    can I use mq2 sensor module without arduino or any microprocessor

  • Abhishek's picture
    Jul 01, 2018

    How much will it cost?? Please answer because I have to make it for my school project.

  • Aswinth Raj's picture
    Aswinth Raj
    Jul 04, 2018

    It will not cost much. Assuming you are from India, the whole project should be completed for less than 300INR

  • Rezk Mattar's picture
    Rezk Mattar
    Jul 27, 2018

    I have a tyco smoke detector (24vdc) & would like to get an output (24vdc) to drive a relay whenever it detects smoke.
    Can you please describe & draw the needful circuit.

  • Onyx's picture
    Oct 12, 2018

    Badly need help can bc547 be replace with MOSFET ?, if ever what MOSFET 

  • Aswinth Raj's picture
    Aswinth Raj
    Oct 15, 2018

    Why with mosfet?

    BC547 is easily available, if you did not find one there are manu alternative transistor like 2n2222 for instance.

    But for some reason if you need a mosfet there, you can use logic level mosfet like IRLZ44N

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