Smoke Detection Alarm kit (Assembled), 100% Tested



In this project, we have designed Smoke Level Detector using MQ-135 Sensor for measuring the level of smoke in the environment. Simply we have interfaced MQ-135 Gas Sensor module with Relay and Buzzer. The Smoke sensor we used is the MQ-135 sensor. Smoke Detectors are very useful in detecting smoke or fire in buildings, and so are the important safety parameters.

Smoke Detector Circuit which not only senses the smoke in the air but also reads and displays the level of Smoke in the Air. This circuit triggers the Buzzer when Smoke level becomes higher than the desirable limit, this threshold value can be changed in the Circuit  according to the requirement.


MQ-135 Module sensor has lower conductivity in clean air. When the target combustible gas exists, the sensor’s conductivity is higher along with the gas concentration rising. Convert change of conductivity to correspond output signal of gas concentration. MQ135 gas sensor has high sensitivity to Ammonia, Sulphide and Benzene steam, also sensitive to smoke and other harmful gases. It is with low cost and suitable for different applications such as harmful gases/smoke detection.

Working –


The MQ-135 smoke sensor consists of a tin dioxide (SnO2), a perspective layer inside aluminum oxide microtubes (measuring electrodes) and a heating element inside a tubular casing. The end face of the sensor is enclosed by a stainless steel net and the backside holds the connection terminals. Smoke is emitted from the source by burning anything. With the smoke cascade on the tin dioxide sensing layer, the resistance decreases. By using the external load resistance the resistance variation is converted into a suitable voltage variation.

Circuit Diagram