In this an Arduino Smoke Level Detector is build using MQ-135 Sensor for measuring the level of smoke in the environment. Simply we have interfaced MQ-135 Gas Sensor module with Arduino and if the gas is above the thresholdValue we have given it will make an alert sound with the buzzer.
Instead of MQ-135, you can use MQ2, MQ3, MQ5 module as well. Basically they all have similar functions.