Gas & Air Quality Sensors

Gas and air-quality sensors detect smoke, LPG, alcohol, CO2, VOCs and dust for leak alarms, room monitors and air-quality stations.

  • MQ sensors (MQ-2, MQ-135 and others) use a heated element whose resistance changes with the gas around it. Most modules give an analog output for the level and a digital output that switches at a threshold set by a potentiometer.
  • For real CO2, the MH-Z19B and MH-Z19E are NDIR sensors that measure carbon dioxide directly; the MH-Z19B reports it over UART.
  • The PMS5003 counts PM2.5 particles for dust and smoke monitoring.

How to choose:

  • Start from the gas you care about. Each MQ number targets different gases.
  • Decide whether you need a trend, which any of these give, or a calibrated number, which needs more care.

Heated sensors need a warm-up before readings settle, and most need calibrating in clean air. They work with Arduino and ESP32. Treat a DIY gas alarm as an early warning, not a certified safety device.

Frequently asked questions

Which MQ sensor should I buy?

It depends on the gas. Each MQ number targets different gases, such as smoke and LPG, or air quality.

Can an MQ sensor measure CO2?

Not reliably. For carbon dioxide use an NDIR sensor such as the MH-Z19B, which measures CO2 directly.

Why do readings drift at first?

Heated sensors need a warm-up period, and calibration in clean air, before readings settle.

Can a DIY gas sensor replace a certified alarm?

No. Use it as an early-warning project, not a safety device.

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