I didn’t find Zigbee CO2 sensors to connect to Home Assistant that didn’t require soldering or the simplest of coding (and I don’t have time to learn either) (e.g. CO2 (carbon dioxide) Zigbee sensor | DIY zigbee devices ) although this looks the most promising: https://titanproducts.com/product/zigbee-3-0-room-co2-humidity-temperature-sensor-tpzrco2ht-z3/
For the benefit of others, here are my top CO2 monitors for monitoring coronavirus exposure risk in offices/public places:
Battery powered
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Aranet4 - £192 - NDIR sensor, visual display, +/-30ppm or 3% up to 5000ppm. Connects to app, data downloadable but bugs reported. Seems to one of two recommended for schools in Ireland. The Pro version connects to proprietary network ecosystem which is aimed at big building BMSs.
https://aranet.com/product/aranet4-sensor/
UK sales: Aranet4 HOME Sensor | LOWEST UK Price £160 | Duomo (UK) -
RS Data logger. £190 NDIR sensor, ±75ppm(0-2000ppm)/±8%(2000-9999ppm), USB connection for download. Mains or battery operated. https://uk.rs-online.com/web/p/air-quality-monitors/2121726
Mains powered
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Netatmo - £110 - Looks nice, app, downloadable, other sensors available in ecosystem.
Accuracy: ± 50 ppm (from 0 to 1,000 ppm) or ± 5% (from 1,000 to 5,000 ppm) Full specifications for the Smart Indoor Air Quality Monitor | Netatmo -
Vision - £129 delivered - NDIR sensor, visual display, mains powered, connects by USB for 30 days data download. Also recommended for Irish schools (no UK strategy in place yet!). ±40 ppm +3% @ NTP. https://www.vision-co2monitor.co.uk/