Test a CO2 Monitor

Thousands of people across Europe have been sold fake CO2 monitors.

Is your monitor fake?

These fake devices cannot detect CO2 and do not give the standardised, meaningful measurements of air quality that a CO2 monitor provides.

Breathing directly on the monitor cannot be used as a test. The water vapour present in your breath at close range will trigger the simple (non-CO2) sensor in the fake devices.

Instead, we have developed two simple and reliable tests to help you identify a fake.

Dissolving Tablet Test

Use an effervescent tablet to fill a bag with CO2. Genuine monitors will detect this; fakes will not.

You will need:

  • A large plastic bag
  • A cup or glass containing a 1 cm depth of water
  • An effervescent tablet of painkiller or vitamin (these "fizz" in water by releasing CO2 gas)

  1. Put the tablet in the glass of water and seal it inside the bag, with the monitor outside.
  2. Wait about 2 minutes for the tablet to dissolve and fill the bag with gas.
  3. Open the bag briefly, put the monitor inside, then reseal it.
  4. Wait 30 seconds: genuine monitors will measure a rapid CO2 increase (by more than 100 ppm).

Alcohol Gel Test

Fake monitors respond to alcohol hand sanitiser gel, while genuine CO2 monitors do not.

The effect is so strong that the enclosing bag is often not required.

You will need:

  • A large plastic bag
  • Alcohol gel (hand sanitiser)
  • Paper tissue

  1. Ensure the bag is fully aired out after the tablet test.
  2. Place the monitor and a paper tissue in the bag, separated by about 5 cm.
  3. Put a small amount (about 1 dessert-spoon) of alcohol gel on the tissue and seal the bag.
  4. Wait 30 seconds: genuine monitors will not respond significantly (less than 50 ppm increase).

The Result

  • If the monitor responds to the tablet but not to the gel: it is likely to be a genuine CO2 detector.
  • If it responds to the gel but not the tablet: it is probably using a VOC sensor which cannot detect CO2.