any smoke around it. A MQ2 smoke/gas sensor is used in the circuit to detect smoke. This sensor/circuit can also be used to detect several other inflammable gases like Methane, LPG, Propane, Alcohol, Butane, Hydrogen and any type of smoke.

The circuit is built around a LM358 operational amplifier IC that is used here in comparator mode. A 2N4401 transistor is used at the output of LM358 to drive the alarm circuit. The alarm circuit is built with a UM66 CMOS melody IC.

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Smoke detectors are very useful devices, they provide very early indication of fire due to which it is possible to take an immediate action to prevent subsequent damages. The circuit shown here is very simple to build, it will activate a loud alarm when the smoke sensor detects
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Smoke Detector Alarm Circuit Diagram