Sensirion SCD40
Also known as: SCD40 · Air quality
The SCD41's cheaper sibling: identical real-NDIR measurement over the 400–2000 ppm range that indoor-air automations actually use.
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At a glance
⚑ flag an error| Measures | co2, temperature, humidity |
|---|---|
| Accuracy | TRUE CO2 (photoacoustic NDIR), 400–2000 ppm |
| Interface | I2C @ 0x62 |
| Supply | 2.4–5.5 V |
| Battery-viable | No (continuous draw) |
| ESPHome | Native ESPHome component — scd4x |
| Typical price | $8-13 (street, varies) |
Compare all sensor modules in one table →
Which one do I buy?
vs SCD41: see the SCD41 entry — the 41 is the safer default; the 40 wins when the price gap is real.
Clone check
Low clone risk. Buy from any reputable listing.
Good for
Gotchas to know
- Range tops out at 2000 ppm — fine for 'open a window', limiting for grow rooms or incident logging.
- No single-shot low-power mode: mains/USB power builds only.
- Same ASC calibration caveat as the SCD41.
Wiring it up
It's I2C, so it shares two pins with every other I2C sensor you own — chain your climate/light/CO2 stack on one bus and mind the address clashes (this one lives at 0x62). Any ESP32 dev board works.