Air Quality Sensors

Air quality monitors measure what you are breathing indoors — particulates, CO2 and VOCs — and turn purifiers or ventilation on before the air gets bad.

What the readings actually mean. PM2.5 measures fine particulates from cooking, candles and outdoor pollution; these are the particles small enough to reach deep into the lungs, and it is the single most useful number for deciding when to run a purifier. CO2 is a proxy for ventilation rather than a toxin at household levels — above roughly 1,000 ppm most people notice drowsiness and poorer concentration, which is why bedrooms and home offices are the rooms worth monitoring. VOCs cover the gases released by paint, cleaning products, furniture and cooking, and are usually reported as an index rather than an absolute figure.

Sensor type matters more than brand. For CO2, insist on a true NDIR sensor. Many cheaper monitors advertise "eCO2", which is estimated from VOC readings rather than measured, and it drifts badly — an eCO2 sensor can report a spike because you opened a bottle of cleaner. NDIR sensors cost more and are the only ones worth acting on.

Where to put it. Breathing height, away from windows, doors and the cooker. A monitor on a kitchen worktop will spend its life reporting cooking spikes and tell you very little about the rest of the house. Bedrooms usually give the most actionable data, because that is where you spend eight uninterrupted hours.

Automating on the readings. The obvious pairing is a purifier that turns on above a PM2.5 threshold. The more useful one is ventilation: a CO2 reading that triggers an extractor or a notification to open a window costs nothing to set up and addresses the problem at source rather than filtering it.