This smoke sensor module with MQ2 Smoke sensor have both digital and analog outputs , you also can adjust the sensitivity with the potentioneter.

PIN Connection

4 pins as follows:

• VCC    (5 V)
• GND (ground)
• Aout (Analog output)
• Dout (Digital output)

When connect to arduino, use digital pins in digital mode (high or low) and use analog pins for analog mode (diffrenet value for different smoke intensity).