Gravity: Electrochemical O2 Sensor (0-25%Vol, I2C & UART)

Grove - Air quality sensor

Grove indoor-air-quality sensor for a broad mix of CO, alcohol, acetone, thinner and formaldehyde. Single analog index, not a calibrated ppm reading.

BME680 Breakout - Air Quality, Temperature, Pressure, Humidity Sensor

MQ-2 Gas Sensor

Combustible gas and smoke sensor: LPG, propane, methane, alcohol, hydrogen and smoke response. Analog output plus a digital threshold pin. Needs heater preheat.

MQ-3 Gas Sensor

Alcohol-biased MOX sensor for ethanol vapour and breath-alcohol style prototypes. Analog output plus a digital threshold pin. Needs heater preheat.

MQ-135 Gas Sensor

Broad indoor-pollutant MQ sensor biased to NH3, NOx, benzene, smoke and CO2-style response. Analog output plus a digital threshold pin. Needs heater preheat.

Particulate Matter Sensor - SPS30

Sensirion SPS30 optical particulate sensor. Use for PM monitoring, not as a VOC/eCO2 or combustible-gas substitute.

Particle, VOC, Humidity, and Temperature Sensor - SEN54

Sensirion SEN54 combined module: particulate matter plus VOC, humidity and temperature. Useful upgrade path from PM-only designs, but firmware and airflow change.

SparkFun Air Quality Sensor - SGP40 (Qwiic)

Sensirion SGP40 Qwiic VOC-index sensor. Good for IAQ trends over I2C, not a gas-specific ppm sensor and not true CO2.

SparkFun Indoor Air Quality Sensor - ENS160 (Qwiic)

ENS160 Qwiic indoor-air-quality sensor with AQI, TVOC and eCO2-style outputs. Not a true CO2 sensor and not an MQ drop-in.

Fermion: ENS160 Air Quality Sensor - TVOC/eCO2/AQI (Breakout)

ENS160 breakout with TVOC, eCO2 and AQI outputs over I2C/SPI. Similar sensing class to ENS160 Qwiic boards, but connector and board format differ.

Fermion: BME688 AI Environmental Sensor (VOC, Temperature, Humidity, Pressure)

BME688 multi-environment sensor: VOC plus temperature, humidity and pressure. Does not replace particulate or direct CO2 measurement.