| 1 | Optical particulate matter sensor | Suspended particles or droplets, often reported in particle-size bands or estimated mass concentration | Light scattering from particles passing through an illuminated sensing volume | Can register changes when aerosol is present in the sampled air | Does not identify the aerosol source; readings can be affected by humidity and other particles |
| 2 | Metal-oxide semiconductor VOC sensor | Broad changes in concentrations of certain volatile compounds | Gas-induced changes in the electrical resistance of a heated metal-oxide sensing layer | May provide a general VOC-related signal for combined monitoring systems | Typically cross-sensitive to multiple gases; a signal is not proof of vaping or a specific compound |
| 3 | Photoionization detector (PID) | Ionizable volatile organic compounds, generally as a broad response | Ultraviolet light ionizes compounds with ionization energies below the lamp energy; the resulting current is measured | Can be used to monitor changes in some VOCs in air | Does not measure all VOCs and does not normally identify individual compounds without additional analysis |
| 4 | Electrochemical carbon monoxide sensor | Carbon monoxide (CO) | An electrochemical reaction produces a current related to the gas concentration | Useful for indoor air-safety monitoring as part of a broader sensor system | CO is not a specific marker of vaping; it should not be used alone to detect vaping |
| 5 | NDIR carbon dioxide sensor | Carbon dioxide (CO₂) | Measures infrared absorption at wavelengths associated with CO₂ | Can supply room-ventilation or occupancy context for environmental monitoring | Does not directly detect vaping aerosol |
| 6 | Formaldehyde sensor | Formaldehyde (HCHO), when the sensor is designed and calibrated for it | May use electrochemical, metal-oxide, or optical measurement, depending on the sensor design | Can support targeted indoor-air-quality measurements | Performance and selectivity vary by design; presence alone does not establish a vaping source |
| 7 | Temperature and relative-humidity sensor | Air temperature and relative humidity | Electronic temperature and humidity elements, commonly resistive or capacitive | Provides environmental context and helps interpret particle-sensor readings | Does not detect vaping; humidity can influence some particle measurements |
| 8 | Differential-pressure or airflow sensor | Pressure difference or air movement through a defined flow path | Measures pressure across a restriction or uses a thermal airflow element | Can monitor airflow in an instrument or device when integrated into a suitable design | Airflow alone does not show what substance is present or whether vaping occurred |
| 9 | Photoelectric smoke detector | Light-scattering or light-obscuration changes in a detection chamber | A light source and photosensor detect changes caused by airborne particles | Some aerosol events may affect readings, depending on the detector and conditions | Designed for smoke/fire detection, not vaping identification; performance with vaping aerosol is not consistent enough to infer a source |
| 10 | Electrochemical gas sensor array | One or more target gases, depending on the installed sensing cells | Gas-specific electrochemical reactions generate measurable electrical signals | Can combine selected gas measurements with particle and environmental data | Each channel has specific targets, calibration needs, and potential cross-sensitivities; the array is not automatically vaping-specific |