Air quality and damp control that works with Home Assistant

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The affordable route to CO2 monitoring: a genuine NDIR sensor (Sensirion SCD40) plus temperature and humidity on a big desk display for around £60 — half the price of an Aranet4. Reviewers cross-checking it against calibrated meters report readings within about 5%, respectable for this price. The catch is Bluetooth: it only talks to whatever's nearby, so anywhere outside your HA host's BLE range needs an ESPHome proxy or USB Bluetooth adapter in the same room. Best sited in a bedroom or home office, where stale air affects sleep and focus — keep it on a desk away from doors and vents, not a draught. No SwitchBot hub required.

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A tidy bedroom monitor that tracks temperature, humidity, CO2 and noise, with the noise reading being the unusual one for sleep: you can see whether a 3am spike coincided with a restless night. It is a cloud product, so readings go through Netatmo's servers, and the UK page showed it as 'Out of stock' at £109.99 when checked. Netatmo offers an app with Asthmatic, Baby and Family profiles, but the HA integration only gives you raw sensor values.

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A genuine CO2 plus PM2.5 monitor for £25 is unheard of — under half the SwitchBot Meter Pro CO2's £60 and a sixth of the Aranet4's £169, and IKEA's collaboration with Sensirion (the same sensor maker behind SwitchBot's chip) suggests this isn't a budget knock-off sensor, just a budget price. It speaks Matter over Thread, so it drops straight into HA's Matter integration with no IKEA hub needed if you already have a Thread border router. At a compact 40 x 40 x 90mm it suits a shelf or windowsill; keep it clear of doors, vents and direct sun. Sells out fast at IKEA UK.

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The most Home Assistant-friendly indoor air quality monitor we've tested: open-source hardware and firmware, a native local-polling integration that Home Assistant discovers on its own, and a tick-box at setup that stops it ever talking to AirGradient's servers. It measures far more than the cheap CO2 meters — CO2, PM1/2.5/10, a VOC index, a NOx index, temperature and humidity — with named, replaceable sensor modules (SenseAir S8, Plantower PMS5003, Sensirion SGP41 and SHT40) rather than an anonymous chip. The catches are UK-specific: there is no UK retailer, so you order direct from Thailand in US dollars and pay the VAT at checkout, which lands the assembled unit at roughly £200. The 1.3in OLED is small, and the 131mm square footprint is big next to an Apollo AIR-1 or Aranet4. Buy it if you run Home Assistant and want CO2, particulate and VOC data driving real automations; buy a SwitchBot Meter Pro CO2 or IKEA Alpstuga if you only want a CO2 number on a shelf.

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The reference-grade NDIR CO2 monitor: years on two AA batteries, an always-on e-ink display, and a core Home Assistant integration reading it passively over Bluetooth (enable "Smart Home integrations" in the Aranet app first). At around £189 it costs roughly three times the SwitchBot Meter Pro CO2 on this site, and the gap is calibration pedigree: Aranet's NDIR sensor is rated to ±(30 ppm + 3% of reading), tighter than SwitchBot's ±(50 ppm + 5%), and is the sensor independent reviewers reach for to sanity-check cheaper monitors against. Buy this for a CO2 number you trust without question; SwitchBot trades accuracy for half the price.

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The no-display sibling of the SNZB-02D and the cheapest accurate room sensor worth buying: ±0.2°C Swiss-grade sensor, a CR2477 that genuinely lasts years, and first-class Zigbee2MQTT/ZHA support — no Sonoff bridge needed despite the marketing. At 45×45×17.7mm it's small enough to tuck on a shelf or wall in every room without becoming a fixture, unlike the -02D's chunky 2.5-inch display unit. It reports within 5 seconds of any change and at least hourly otherwise, so Home Assistant automations react fast. Buy the -02D only if you want one glanceable reading on a desk; for whole-house heating zoning, scatter several of these instead.

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SwitchBot's Outdoor Meter is a battery sensor with no screen — pair it with the app or an HA dashboard for readings, since there's nothing to check on the unit itself. It runs roughly two years on its AAA batteries before a swap, and Bluetooth range is rated to 100m line-of-sight, though expect far less through walls (see the HA integration notes below). The IP65 shell handles rain and dust for genuine outdoor or greenhouse use, and it comes with a lanyard rather than a bracket, so you're hanging it, not screwing it to anything. At £15, still the easiest local-Bluetooth outdoor sensor for HA.

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One of the very few connected air purifiers with genuine local Home Assistant support — it's a straightforward Zigbee device, pairable directly via ZHA or Zigbee2MQTT with no cloud round-trip required, and it doubles as a decent Zigbee router when running on mains power. IKEA's own route is through a DIRIGERA hub and the IKEA Home Smart app, but that's optional if you're already running your own Zigbee coordinator.

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The budget pick to sit alongside IKEA's STARKVIND on this site — a small-bedroom HEPA purifier at a fraction of the price, but it depends entirely on VeSync's cloud and doesn't speak Zigbee or Matter, so treat it as an app-first device that HA can nag at (fan speed, on/off, sleep mode) rather than one you can fully script offline. Home Assistant's official VeSync integration covers the fan and its speed levels reliably, but reported gaps (missing night-light entity, occasional 'unknown device' pairing issues on this exact model) mean it's less polished than the site's Matter/Zigbee purifier picks.

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A larger Xiaomi purifier with a proper laser dust sensor, an OLED display and a high clean-air rate for its size. It is one of the few smart purifiers where HA has a local integration: Xiaomi Miio can talk to it on the LAN using the device token, though that token has to be extracted from the Mi Home account. Cheap to run and well supported, but the setup is techy and filters are an ongoing cost.

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Levoit's compact smart HEPA purifier for bedrooms and small living rooms, with a laser air-quality sensor and auto mode. It runs through the VeSync cloud, so HA control is cloud-polled rather than local. It does the quiet, cheap-filter job well; the compromise is the app dependency. Buy it for the price per cleaned room, and know that HA exposes the basics only.

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A quiet 20 L/day dehumidifier with no official Home Assistant route: the community Duux integration (installed through HACS) lists the Bora and talks to Duux's cloud, so it works only while Duux's servers do and it is unaffiliated with Duux. Dunelm's UK page prices it at £300 and lists a 4 L tank, 36 dB night mode, a carbon filter and rooms up to 40 m². Model ambiguity: the integration lists the 'Bora Dehumidifier (2024)', and the retailer pages we fetched give no model code, so confirm your unit matches.

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Pick this one for the continuous-drainage hose rather than for smart-home polish. Home Assistant has no official support: the route is a community HACS component that talks to the unit over your LAN, but it still needs your Midea cloud login once during setup to fetch a token. Inventor's own EVA II PRO 20L product page never mentions Wi-Fi or an app, only a support link to the Invmate II application, and the Invmate II page names a separate 'EVA II PRO Wi-Fi' model, so make sure the unit you buy is the Wi-Fi variant before assuming any of this applies. Hardware is a 20 L/day R290 unit with a 3 L tank, 260 W draw and 37/40/45 dB(A) on low/medium/high.