Simple Smoke Detector Alarm Circuit

Published  July 19, 2017   19
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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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Submitted by padmanahan on Sat, 11/18/2017 - 12:55


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.

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 

Submitted by SAURABH KESARI on Mon, 12/25/2017 - 10:19


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??

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  

Submitted by Abhishek on Sun, 02/25/2018 - 00:07


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.

Submitted by Sachin on Mon, 04/02/2018 - 18:22


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.

Submitted by Jing on Thu, 05/10/2018 - 21:02


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

Submitted by Wayne Clinton on Sun, 05/27/2018 - 14:40


can I use mq2 sensor module without arduino or any microprocessor

Submitted by Rezk Mattar on Fri, 07/27/2018 - 10:08


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.