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How to reduce COVID-19 risk indoors with sensors you can buy on Amazon.

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The scientific evidence around Covid-19 suggests temperature, humidity and ventilation are key to preventing the indoor spread of coronavirus in the home. Keeping an eye on these conditions at home isn’t as technically tricky as you might think. With winter coming, we want to share our knowledge of sensoring and smart buildings to show you how to use simple technology and take action for a safer home.


COVID-19 and Indoor Air Quality: The Science

There is increased evidence around aerosol transmission of COVID-19. This means that the virus suspends in tiny droplets in the air, like smoke. If room conditions promote viral circulation and build-up then it’s possible to infect many people within the room.

A recently published summary by El Pais demonstrates the expected spread of Covid-19 in different settings. It’s a must read.

Air and indoor air is a big factor in transmission of the virus. And, as we know, winter is coming.



Illustrated indoor air transmission. Credit: El Pais.

The arrival of winter, and with it more time indoors with shut windows and heating on, presents a real driver of increased disease spread. As Orla Hegarty, Assistant Professor at the Department of Architecture at UCD, has been detailing on her twitter account, indoor air quality now has an outsize impact on the spread of the disease.


[Thread] Protecting yourself from viruses ‘is not just about ventilation, it’s about humidity in rooms’ -Dr @laoneill111 on @NewstalkFM #Covid19

& here’s why… 1/

— Orla Hegarty (@Orla_Hegarty) October 31, 2020
A really concise update from Prof. Luke O Neill on the impact of indoor humidity.

Researchers now know that indoor humidity below 20% is great for viral spread of Covid-19 (source). Combined with other findings that suggest ventilation and air flow are also critical, we know that to lower our risk we need to:

  • Keep air cycling and regularly refreshed. (El Pais)
  • Prevent humidity from dropping too far but keep temperatures up. (Source)

Measure Then Manage

The first challenge is to turn the scientific literature into something we can act on. We can’t manage what we can’t measure, so we need to come up with a solution to collect the data we need quickly and simply. This isn’t a tech project, instead it’s a short term intervention to try to reduce the risk of Covid-19 transmission.

We know temperature has an impact on how long the virus survives in the air. The colder it is, the longer the potential for the virus to survive in the air and on surfaces. So we need to keep temperatures up above 15 degrees. In winter this is achieved by heating systems. (Source)

We now know humidity also correlates to the survival of the virus. As Orla Hegarty summarises: “in dry indoor air, droplets with virus dry out faster… & lighter aerosol particles float longer the air; if the room isn’t well ventilated, they build up & spread (like cigarette smoke)” (Source). By keeping relative humidity at 40%-60% or above 60% indoors, these lighter aerosol particles are less likely to develop (Source).

 A relative humidity of 40 to 60 percent could reduce the spread of the viruses and their absorption through the nasal mucous membrane.

Research at Leibniz Institute for Tropospheric Research (TROPOS)

We know air flow and ventilation, turning over old air and moving new air in its place, breaks up the virus and reduces the risk of transmission significantly. This is why we are told to do so much activity outdoors. It’s hard to measure accurately without expensive equipment but one proxy for air flow and turnover is Carbon Dioxide, as the rate increases while we breath, it can be used to conclude the ‘staleness’ of the air. 

Outdoors, CO2 levels are just above 400 parts per million (ppm). A well ventilated room will have around 800 ppm of CO2. Any higher than that and it is a sign the room might need more ventilation.

Prof Shelly miller, The Conversation



This leaves us with a conundrum, heating systems encourage us to ‘seal up the room’ to keep the heat in. This encourages staleness and buildup of virus, it also lowers humidity as warming the air dries it out. So we need to actively manage temperature, humidity and air flow to keep a balance.

Technology can help us to manage this balance. Here we’ve found 3 of the quickest and lowest cost ways of getting the data you need at home. 

NOTE: While temperature and humidity values can be gathered relatively simply, CO2 detection needs to be “at a height where individuals are breathing, and away from sources of fresh air such as an open window, where concentrations are typically much lower than the room average, if one is to obtain an estimate for the load of potentially infectious particles.” (Source)


The Data Trifecta

Key Indicator Metric Sensor Threshold
Temperature Degrees (°C) Thermometer 20 degree
Humidity RH (%) Hygrometer 40% RH
Air Flow/ Freshness CO2 (ppm) IAQ / VOC Sensor 600 ppm
The trifecta of key indoor air data and suggested thresholds.

Sensors to monitor Indoor Temp, Humidity, CO2 at home

This is the tricky part. From a hardware perspective, measuring temperature and humidity is trivial and cheap. Measuring Carbon Dioxide is a more tricky and makes devices little more expensive. Many chip makers sell combined temperature and humidity sensors for use in all sorts of equipment so the market is flooded with those at a variety of price points. Getting Carbon Dioxide on board is less common. So we tried to get a fit for three levels of use:

  • Quick and Private: Let’s just get a device that works at low cost. No need for apps, pairing, fancy alerts just simple actionable data.
  • Mobile Alerts or Remote Monitoring: An approach that lets you get data on your phone through an app either by pairing or streaming over your Wi-Fi.
  • Professional Setup: For a larger floorplan or more complex use case, some suggestions for professional monitoring and alerting.

Quick and Private

You can’t go wrong with a combined sensor that does all three jobs. It’s not smart, it just plugs in, measures the data and shows results on the device screen. Unfortunately it’s pricey enough when you are trying to get a 3-metric combo.

This unit on Amazon is unrated so buyer beware, it’s £73.99.

A lot of these units are coming from China so AliExpress might be fruitful if you want to go direct to source. This unit ships from within the EU – Czech Republic – and comes from a family of environmental monitors. The more rooms you have the more you have to buy. As none of these connect to the internet there is no privacy concerns with this approach.


Mobile Alerts or Remote Monitoring

If you want to be alerted when things are not going to plan or want your indoor air quality readings at your fingertips, then you will want a smarter device and an app to go with it. It’s hard to look past the Netatmo Smart Indoor Air Quality Monitor for €99 / £89.

51NO0x0qIfL. AC SL1000

The sensors have excellent sensitivity (incl. +/- 50ppm on the CO2) and the app is free for life, no ongoing subscription. You can add more devices per rooms and scale as you need. It ticks all the boxes and enables you to remotely keep an eye on conditions or receive alerts on the go.

As usual the cheapest route is to remove CO2 detection. With only temperature and humidity monitoring you can spend less than £20/€25. With the Govee sensor linked below you do lose the benefit of knowing when your air is stale, but that’s a call you can make depending on your own situation. The app uses Bluetooth pairing to share data so real time alerts are unlikely.

Professional Setup

If you have an essential workplace that is still on the go, or you are hoping to reopen your gym, cafe or office safely when restrictions ease, you may want to lower the risks to your staff and clients. Unfortunately, smart home equipment isn’t always going to scale for commercial operations as Floorspace is generally too big.

You’ll need a lot of devices and all that data needs to be streamed wirelessly to cut costs. A very easy way to set about achieving this is deploying a LORAWAN gateway with good power and using off the shelf sensors like the ELSYS CO2 Lite to gather temp, relative humidity and carbon dioxide from points across your workplace. LORAWAN is a wireless system for sharing data between sensors to a central gateway. The gateway then pushes the data online so you can use it in a dashboard or application online.

If you get a sensor setup going, the temperature, humidity and CO2 data will need to be integrated on a dashboard like Thingsboard, Datacake or Wia. This involves more work to implement but will be a far more robust setup that spans a large facility (or multiple facilities) with reliable uptime.

Do you want to take steps to monitor air conditions in your business but don’t know how? We can help. Contact us now for more information.

Are you interested in including Covid risk monitoring as part of your stack – let us know today.


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