Carbon Dioxide Monitor MD-21

What is supplied in the box?

CO2 monitor, detachable support stand, micro USB cable (1 metre long), instruction manuals (English, French, German, Dutch). Please note that a USB power source, such as a standard USB mains adapter, is required but not included.

How long does the rechargeable battery last?

Up to 9 hours from fully charged, though this depends on the exact pattern of use (e.g. keeping the display light on uses more power). We recommend that the monitor is left on USB cable power as this allows long-term use without the hassle of recharging.

Where can I use it?

The monitor is suitable for most indoor areas, including homes, offices, classrooms, clinics, cafes and restaurants. It is designed to be used long-term in a single location.

Does it have a bright display screen?

The monitor has a bright light emitting display. To avoid distraction, or for use in dark rooms, you can disable (darken) the screen with a single button press. In this state, the coloured indicator light flashes briefly every five seconds. The monitor continues to measure CO2 and will still alert you to high levels.

What room size is it suitable for?

It is suitable for all room sizes. In large rooms, use one monitor for every 120 square metres of floor area.

Does it have an alarm?

It has an audible and visual alarm which triggers when the CO2 level rises above the alarm threshold. You can disable the alarm sound by muting the monitor with a single button press.

Can I change the alarm threshold levels?

Yes. The user guide explains how to change the green-yellow threshold and the yellow-red threshold, which is also the audible alarm trigger. These can be set to any value in the range 0–5000 ppm in 50 ppm steps.

Can it be calibrated?

Yes: fresh outdoor air gives a reliable baseline of 420 ppm CO2. Follow the manual calibration procedure (described in the user guide) before the first use. This simple process corrects for small changes that occur during shipment of the monitor to you. After that, the monitor ensures ongoing accuracy by performing automatic self-calibration.

Does it use an NDIR sensor?

Yes, the monitor uses a non-dispersive infrared sensor (NDIR). NDIRs are the best technology for compact and accurate consumer CO2 measurement.

Is it accurate?

Yes. The monitor has a measurement accuracy of ±50 ppm ±3% of reading. Indoor CO2 levels have a typical range of 1000 ppm, so the monitor can reliably distinguish healthy and unhealthy levels.


Which countries do you deliver to?

We deliver to addresses in mainland Great Britain and Northern Ireland. We dispatch from warehouses in the UK, so your order will not cross a customs border.

When will my order arrive?

Standard (free) delivery: orders are dispatched within 2 business days and typically delivered within an additional 3 business days.
Express delivery: orders are dispatched within 1 business day and typically delivered within an additional 1 business day.
Please allow for longer delivery times during busier periods (such as Christmas).

How can I track my delivery?

You will receive an email at the time of dispatch containing a tracking link giving more information about your delivery.

How much does delivery cost?

Standard delivery (3-5 business days from order) is FREE for all orders.
Express delivery (1-2 business days from order) is £3.00 per order, unless otherwise stated at checkout.

The tracking information shows "delivered" but I haven't received anything.

If you are not at the delivery address when your order is delivered, our courier may leave your item in a safe place for you. Please check possible safe places around your delivery area, including with neighbours. Please contact us if you are unable to find your parcel.

I have other questions about delivery.

Please check our Delivery Policy or contact us.


Is the checkout secure?

Yes: we use an industry-standard secure payment processor. We do not see or store your card details.

I have a discount code: where do I input it?

Discount codes can be entered at the checkout (the step after the shopping basket).

How do I return an item?

Start the returns process by contacting us as soon as possible, stating your email address and details of the return. For more information, see our Returns & Refunds policy.

When will I receive an order confirmation?

You will receive an acknowledgement email immediately after placing your order. You will later receive a confirmation email when your order is dispatched. Please check your spam/junk folder if you have not received these.

My order arrived damaged, incorrect, or with an item missing. What should I do?

Please contact support@metriful.com with a clear image of your delivery note and the damaged/incorrect item (if applicable) and we will resolve this for you.

I have other questions about ordering.