Bosch BME680

4-in-1 environmental + VOC gas sensor

The Bosch BME680 is the sensor we hand to almost everyone, because it does four jobs at once: a metal-oxide gas element for VOC/air-quality, plus precision temperature, humidity and barometric pressure — all over I²C or SPI on a board with onboard regulation that runs happily at 3.3 V or 5 V. Bosch’s BSEC library turns the raw gas resistance into a usable Indoor Air Quality (IAQ) index, so a single ESP32 can drive a whole environmental dashboard. It won’t name individual gases, but as an all-rounder for IoT loggers and smart-home builds, nothing this size matches it.

Sensirion SCD41

Photoacoustic NDIR true-CO₂ sensor

When you need a number you can actually trust, the Sensirion SCD41 is the one. It uses photoacoustic NDIR sensing to measure real CO₂ concentration — not the “equivalent CO₂” that VOC sensors estimate — over a wide 400–5000 ppm range, with onboard temperature and humidity and simple I²C output. It’s the gold standard for ventilation studies, classroom CO₂ monitors and “is this room stuffy?” IoT projects, and the linked Sensirion evaluation kit ships with cables to get you reading ppm in minutes. The only catch is price: this is the most expensive pick here, and deservedly so.

3. Sensirion SGP30

TVOC + eCO₂ · I²C · calibrated MOX

The SGP30 from Sensirion is a fully calibrated multi-pixel MOX sensor that returns a TVOC reading plus an estimated eCO₂ over I²C — no analog math, no per-board calibration. Unlike the CCS811 it doesn’t need I²C clock stretching, so it works cleanly with the Raspberry Pi, and it accepts a humidity value from a companion sensor for better accuracy. It’s the easiest way to add a credible “air freshness” number to a dashboard.

4. Winsen MH-Z19B

NDIR CO₂ · UART/PWM · 0–5000 ppm

The MH-Z19B brings genuine NDIR CO₂ sensing within reach of a hobby budget. It outputs real CO₂ over UART (and PWM), has built-in temperature compensation and self-calibration, and is the sensor behind countless DIY “CO₂ canary” builds. Accuracy and long-term stability don’t match the SCD41, but for logging room CO₂ on an ESP32 or Pi it’s a fantastic value — just disable auto-baseline calibration if the sensor never sees fresh ~400 ppm air.

5. Plantower PMS5003

Laser PM1 / PM2.5 / PM10 · UART

If your project is about dust, smoke or smog rather than gas, the Plantower PMS5003 is the maker favourite. A tiny fan draws air past a laser, counting particles to report PM1.0, PM2.5 and PM10 concentrations over UART — the same metric air-quality indices are built on. It’s well supported on Raspberry Pi and Pico, ships with a cable, and is the heart of citizen-science monitors worldwide. Remember it’s a 5 V device with 3.3 V logic, and give the fan ~30 seconds to stabilise.

6. MICS-6814

CO · NO₂ · NH₃ (3-in-1 MEMS)

The MICS-6814 packs three MEMS sensing elements into one package to track reducing (CO), oxidising (NO₂) and NH₃ gas groups at once — ideal for pollution and agricultural/vehicle-odour monitoring. It’s sensitive to hydrogen, ethanol and hydrocarbons too. Treat it as qualitative: without lab calibration you get clear up/down trends per channel rather than certified ppm. Generic Amazon boards expose analog outputs (you’ll need an ADC), while breakout-garden style boards add an MCU for I²C.

7. CCS811

eCO₂ + TVOC · I²C · ultra-low power

The CCS811 is a low-cost MOX gas sensor that reports estimated eCO₂ (400–8192 ppm) and TVOC over I²C, with a tiny footprint and configurable interrupt. It’s a popular budget alternative to the SGP30 and pairs nicely with a separate temp/humidity sensor for compensation. The catch: it uses I²C clock stretching, which trips up some boards (notably the Raspberry Pi’s default I²C), and it needs a long burn-in. If your MCU handles clock stretching, it’s a cheap, capable VOC sensor.

8. MQ-2

Smoke · LPG · methane · H₂ · CO

The MQ-2 is the classic “my Arduino can smell smoke” module — a heated metal-oxide sensor on an LM393 board with both an analog output (concentration trend) and a digital threshold output set by an onboard potentiometer. It responds to LPG, propane, methane, hydrogen, alcohol, smoke and CO between roughly 200–10,000 ppm. It can’t identify which gas it’s seeing, but for leak alarms and fire-detection demos at a couple of dollars, nothing is more accessible.

9. MQ-135

NH₃ · NOx · benzene · smoke · CO₂

The MQ-135 is the budget go-to for generic “air quality” projects, reacting to ammonia, NOx, alcohol, benzene, smoke and CO₂ with analog and digital outputs. You’ll see it in countless DIY air-quality meters that map its analog value to an arbitrary “AQI” number. Be honest about its limits: those ppm conversions floating around online are rough estimates from the datasheet curve, not calibrated truth. As a cheap trend indicator and a great way to learn the Rs/Ro calibration method, it’s hard to beat.

10. MQ-7

Carbon monoxide · 20–2000 ppm

The MQ-7 is the budget specialist for carbon monoxide, sensing roughly 20–2000 ppm CO with analog and digital outputs. For best results it’s meant to be cycled between a high (5 V) and low (1.4 V) heater voltage, so a quality build or a little PWM/MOSFET work pays off. It’s a superb learning tool and a fun maker CO “early-warning” project — but treat it as educational. For protecting people, always use a certified UL-listed CO alarm, not a hobby module.