Indoor Air Sensors: Which Measurements Actually Matter

Indoor air quality monitors are now as common as smart thermostats. But if you buy a cheap one, you might just be buying a random number generator. To get actionable data, you need to know which sensors matter and which ones are just marketing fluff.

1. PM2.5 (The Health Critical Metric)

What it is: Particulate Matter smaller than 2.5 microns. This is the stuff that gets deep into your lungs and bloodstream (smoke, cooking fumes, fine dust).

• The Sensor: Look for a "Laser Particle Counter". It uses a laser to count dust motes in the air.
• Action: If this spikes, turn on your HEPA purifier or stop frying bacon.
• Target: Keep it below 10 µg/m³. Above 35 is unhealthy.

2. CO2 (The Ventilation Metric)

What it is: Carbon Dioxide. It builds up when people breathe in a closed room.

• The Sensor: You must get an NDIR sensor. Avoid "eCO2" sensors, which just guess based on smells.
• Action: If it hits 1000 ppm, open a window.
• Target: 400-800 ppm is ideal.

3. VOCs (The Chemical Metric)

What it is: Volatile Organic Compounds (chemicals from paint, cleaning sprays, new furniture).

• The Reality: Consumer VOC sensors are "relative," not absolute. They can tell you "something changed" (like you just peeled an orange), but they can't tell you if it's dangerous formaldehyde or harmless citrus oil.
• Usefulness: Low. Use your nose instead. If you smell chemicals, ventilate.

4. Radon (The Silent Killer)

What it is: A radioactive gas from the ground. It is the #2 cause of lung cancer.

• The Sensor: Specialized electronic radon detectors (like Corentium) or one-time lab tests.
• Action: Every basement should be tested once. If high, you need professional mitigation, not just a window fan.

5. Humidity & Temp (The Basics)

Cheap and essential.

• Target: 40-60% Humidity.
• Why: Prevents mold (high) and viruses (low).

Summary

Don't buy an "All-in-One" monitor unless it specifies NDIR CO2 and Laser PM2.5. If the listing is vague, the data will be too.