Indoor air monitor specs
What to look for in a PM2.5 monitor, which extra sensors are worth having, and which aren't.
An indoor monitor is the only way to know whether your clean room works. How to use one is covered in measuring indoor air.
Must have
- Laser / optical particle sensor for PM2.5 (sometimes also PM10)
- Displays PM2.5 in µg/m³, not only a colour or an “AQI”
- Updates every minute or so, so you can see the effect of turning a purifier on or opening a door
Very useful
- Data logging or history (on the device or an app), so you can compare overnight trends
- Battery or USB power, so you can move it between rooms
- Humidity and temperature readout: helps you spot when fog or a humidifier is inflating PM readings
Worth it for bedrooms: CO₂
An NDIR CO₂ sensor (look for “NDIR”, not “eCO₂” or “equivalent CO₂”) shows when a closed room needs airing. Useful for a sealed bedroom with sleepers.
Skip or don’t trust
- “TVOC”, “HCHO” (formaldehyde) and “eCO₂” readings from cheap sensors: these are often estimates from low-cost metal-oxide sensors and can be very unreliable.
- “Air quality score” with no units.
- A purifier’s built-in sensor as your only check: it sits right next to the clean-air outlet and often reads optimistically.
Accuracy, honestly
Low-cost particle sensors are estimates. They’re best at showing changes and trends in the same room, and less reliable for exact numbers, especially in high humidity. If you have two monitors, place them side by side for a day first to see how they compare.