Knows what your room is breathing, and says when to open the window

Morning

Eight hours of sleep and still a heavy head. Usually it is not the coffee but the closed window: by morning a bedroom holds 2000–2500 ppm of carbon dioxide, six times the outdoor level. In a controlled study, people who slept at 850 ppm woke up sharper and more rested.

Strøm-Tejsen et al. Indoor Air, 2016

Working day

In an office with the door shut the air turns heavy within an hour: CO₂ passes 1000 ppm and you crave coffee when what you need is a window. Work goes best at 21–22 °C and 300 lux on the desk; in the heat performance drops by almost a tenth.

Seppänen et al., LBNL; SanPiN 1.2.3685-21

Winter

The heating comes on and the humidity in the flat drops to 15–20 %, desert level. Throats dry out, floors creak, and viruses stay airborne for hours. A humidifier is needed not “in winter in general” but when the screen shows less than 40.

Kudo et al. PNAS, 2019; Arundel et al. 1986

• 80–90 %

  of a city dweller's time is spent indoors — at home, at work, at school, in transit.

  research reviews in the project corpus; the same figure is used by WHO and EPA
• 2500 ppm

  and more of carbon dioxide builds up in a bedroom overnight with the window and door closed. Outside it is about 420.

  Strøm-Tejsen, Wargocki, Wyon. Indoor Air, 2016
• 18 °C

  is the WHO minimum for a home in winter: below it blood pressure and blood viscosity rise.

  WHO Housing and Health Guidelines, 2018
• 15–20 %

  humidity is a normal heated winter apartment — desert level. Mucous membranes dry out and viruses stay airborne for hours.

  Kudo et al. PNAS, 2019; Arundel et al. 1986
• № 2

  environmental cause of ill health in Europe is noise, right after air pollution. The body never gets used to noise at night.

  WHO Environmental Noise Guidelines, 2018; WHO/EEA

FAVEO makes these numbers visible: six sensors in the room, the weather and air outside, and one line on the screen — what to do right now.

Three entries from the same day. On the left what it measured, on the right what it said.

• 13:32 · room 841 ppm, +21.5 °C
  outside +21 °C, no rain
  A good moment to open a window

  The room is stuffy; outside is no warmer than inside, and dry.
• 14:02 · room +18.4 °C
  an hour ago +21.5 °C
  The window has been open long enough

  CO₂ is already at outdoor level and the room has cooled by three degrees. Time to close it.
• 23:02 · humidity 46 %, 426 ppm
  noise 46 dB, light 0 lux
  The bedroom is ready for sleep

  Humidity in the middle of the range, fresh air, no light. No humidifier needed tonight.

• CO₂ is high, outside is clean and not hot
  A good moment to air the room: window wide open for 5–10 minutes, the air changes completely, the walls don't have time to cool.
• CO₂ is high, but there is smog or pollen outside
  Keep the window shut: with an air quality index above 100 the air outside is worse than inside. Better a purifier, or wait.
• Hot day, outside warmer than inside
  Close windows and curtains. In the evening, when outside cools below the room, the device will remind you to open.
• Night, 0 lux, noise rising
  The device dims to 15 % and stays quiet. In the morning it shows how much noise and CO₂ there was overnight.

None of the 30 devices we checked turns “room × outside” into ready advice: the others show two numbers side by side and leave the conclusion to you.

1. 

   Carbon dioxide, ppm

   The main sign of a stuffy room. Outside air is about 420 ppm, a fresh room stays under 800, above 1400 it is time to open a window. 4 September: night at outdoor level, people in the room from nine in the morning.

   under 800 — fresh · 800–1400 — getting stuffy · above 1400 — open a window

   In a controlled trial people slept worse at 2400–2600 ppm and were sleepier by day than at 850. CO₂ itself is not a poison: it is the most honest sign that a room has not been aired for a long time.

   Strøm-Tejsen et al. Indoor Air 2016; GOST 30494-2011; EN 16798-1
2. 

   Room temperature, °C

   The air, not the circuit board: the device subtracts its own heat. Living-room comfort by the Russian standard GOST 30494 is 20–25 °C, cooler for sleep.

   20–25 °C — comfortable · 18–20 and 25–28 — attention

   Above 24–25 °C sleep fragments: less deep and REM sleep. Below 18 °C in winter blood pressure rises. Peak work performance is around 21–22 °C; at 30 °C it drops by almost a tenth.

   WHO 2018; Okamoto-Mizuno & Mizuno 2012; Seppänen, LBNL
3. 

   Relative humidity, %

   In winter with the heating on it drops to 20–30 %: dry throat, cracking floors. Above 60 % in summer — mould and dust mites. The device tells you whether a humidifier is needed today.

   40–60 % — comfortable · 30–40 and 60–65 — attention

   At 40–60 % viruses, mould and dust mites are all at their lowest. Below 50 % dust mites die within 4–11 days. Above 60 % mould grows in corners and on windows.

   Arundel et al. 1986; WHO Dampness and mould 2009; Kudo et al. PNAS 2019
4. 

   Barometric pressure, hPa

   Shown for reference with a three-hour trend. There is no health norm for pressure, so there are no coloured zones here.

   a change of 3–4 hPa in 3 hours is noted in words

   The link between pressure and how people feel was studied in 1.5 million patients and not found: no link with joint pain, a weak and unreproducible one with migraine. So the device shows pressure and its trend, but no coloured verdicts.

   Jena et al. BMJ 2017; Okuma et al. 2015
5. 

   Estimated noise level, dB(A)

   The microphone measures level only, no audio is recorded. A quiet bedroom at night is under 30 dB, a conversation about 55. Not a certified sound meter, but it sees quieter and louder honestly.

   day under 40 dB, night under 30 — quiet

   Every +10 dB of night-time noise slightly raises the risk of hypertension, heart attack and diabetes in large cohorts. You cannot get used to noise at night: the pulse jumps even in people who “stopped noticing” the road years ago.

   Münzel et al. Eur Heart J 2014; WHO Community Noise 1999; SanPiN 1.2.3685-21
6. 

   Illuminance, lux

   0 lux at night, a bright room by day is 150 and more. This sensor dims the screen in the evening and tells the device you have gone to bed.

   150 lux and up by day — enough for reading and work

   Ordinary room light in the evening, under 200 lux, delays melatonin onset in almost everyone and shortens its night by an hour and a half. Just 5 lux in the bedroom at night doubled the risk of depression in a large cohort. By day, though, there is usually too little light: 300–500 lux against 100,000 outside.

   Gooley et al. JCEM 2011; Obayashi et al. HEIJO-KYO; Brown et al. PLOS Biol 2022

Market research, July 2026, from manufacturer sites and independent reviews; “n/a” — not confirmed in the research. FAVEO and SwitchBot use the same SCD40 sensor; the difference is the screen and the fact that SwitchBot passes CO₂ to Apple Home only through a hub. Estimated eCO₂ in cheap devices is off by hundreds of ppm: it is calculated from volatile compounds, not measured.

Dead clouds

In 2022 Awair switched off its first-generation devices — working sensors became useless. In May 2026 the Netatmo cloud went down and people could not see data from sensors in their own homes. FAVEO stores and shows everything itself.

A screen, not an app

People check the app for the first two weeks and the device screen for years. Airthings shows data only in the phone; the Aranet screen is the size of a matchbox.

Honest CO₂

Marketplaces are full of “CO₂ stations” for a few dollars where CO₂ is guessed, not measured. Reviewers agree: only an infrared sensor is worth buying.

All of it is stored on the device and shown on its own screen or on a phone via QR code.

Who it is for

• 

  Bedroom

  By morning a closed bedroom is at 2000–2500 ppm, and you feel it as grogginess. The device shows what happened overnight and says when to air the room in the evening: the target is 18–20 °C, under 800 ppm, quiet and dark.

• 

  Nursery

  Paediatricians recommend 20–22 °C and 40–60 %; overheating is more dangerous for infants than cool air. Light for homework — 200 lux and up. All of it on one screen, no phone needed.

• 

  Desk

  In an office with the door closed CO₂ passes 1000 ppm within an hour. Peak performance is at 21–22 °C and 300 lux on the desk. The device reminds you to air the room before the headache.

• 

  Allergy sufferers

  Below 50 % humidity dust mites die; above 60 % mould grows. Outside, the device sees PM2.5 dust and will not suggest airing during smog.

• 

  Weather-sensitive people

  Pressure and its three-hour change are on the screen, honestly and without diagnoses. Science has not confirmed a link with how people feel, and the device does not invent one.

Questions

• Does it need the internet?
  Not for measuring. Wi-Fi is used for the weather outside, exact time and updates.
• Do I need an account or an app?
  No. Everything is on the device screen; history opens on a phone via QR code in the browser.
• Why an NDIR sensor and not cheap “eCO₂”?
  It measures CO₂ with an infrared beam; “eCO₂” only estimates it from volatile compounds and is often off by a factor of two or more.
• Where should it stand?
  On a desk or bedside table at breathing height, away from the window and radiator. The light sensor faces backwards, so a wall behind works best.
• Is it a medical device?
  No. It is a household climate monitor. It suggests opening a window or humidifying; it does not diagnose anything.