To detect gases like CO₂, CO, LPG, and smoke, different types of gas sensors are available, each based on specific sensing principles. Here’s a breakdown:

1. CO₂ (Carbon Dioxide) Sensors

Sensor	Type	Features
MH-Z19 / MH-Z14	NDIR (Non-Dispersive Infrared)	High accuracy, UART/PWM output, widely used
Senseair S8	NDIR	Reliable, compact, low power
CM1106SL-NS	NDIR	Digital output, stable over time

Applications: Indoor air quality, HVAC, greenhouses

2. CO (Carbon Monoxide) Sensors

Sensor	Type	Features
MQ-7	Electrochemical/Semiconductor	Cheap, analog output, needs calibration
ZE07-CO	Electrochemical	UART output, higher precision
Figaro TGS5042	Electrochemical	Low power, good for battery apps

Applications: Safety alarms, garages, heating systems

3. LPG (Liquefied Petroleum Gas) Sensors

Sensor	Type	Features
MQ-2 / MQ-6	Semiconductor	Detect LPG, propane, methane; analog output
MQ-5	Semiconductor	Broad hydrocarbon gas detection
MiCS-5524	MOS	Compact, multiple gas detection including LPG

Applications: Kitchen safety, leak detection

4. Smoke Sensors

Sensor	Type	Features
MQ-2	Semiconductor	Detects smoke, LPG, methane, hydrogen
MQ-135	Semiconductor	Sensitive to smoke and indoor air pollutants
Photoelectric Smoke Detector Modules	Optical	Used in commercial fire alarms

Applications: Fire detection, home safety systems

Multi-Gas Sensor Modules

For applications needing multiple gas detection:

Module	Detects	Notes
MQ-2	Smoke, LPG, CO, H₂	Low cost, widely used
MQ-9	CO, methane, LPG	Dual sensor element
CCS811 + SCD30	CO₂, VOCs, temp/humidity	Digital I²C output, good for IAQ systems

Interface Types

Interface	Sensors	Notes
Analog	MQ-series	Needs ADC, calibration, power heating
Digital (UART/I²C)	MH-Z19, ZE07-CO, SCD30	Easier integration, more accurate

What sensors can detect CO2, CO, LPG, or smoke?