HALO is an air quality monitor that shows its working

A sensor node you build, not a product you buy

HALO is described as an open source, ESP32 powered air quality monitor with an RGB ring, a touchscreen and a set of environmental sensors, and the phrase that matters is in the last section of the readme, that the software and the CAD files have been shared so other people can build on them. That makes this a hardware project with a firmware repository rather than a consumer device, and it changes how you read everything else. The firmware installer is published on the project's own pages, the build instructions live in the repository wiki, and the community is a Discord server rather than a support desk. The design centre is the LILYGO T-Display-Long-S3, an ESP32-S3 board with a dual core LX7 microcontroller and a 3.4 inch LCD touchscreen, and the readme is upfront that the device operates on WiFi via ESPHome so that there is no cloud subscription and no hidden fee. The stated motivation is to have a sensor with personality, which is a softer claim than it sounds, since a device with a display and a ring in the room changes how people interact with the reading.

The sensor list is the bill of materials

The hardware section names four sensing parts and what each one adds, and the division of labour is clean. The SCD-41 measures carbon dioxide, temperature and humidity. The SEN54, or the SEN55, covers the particulate side with PM1, PM2.5, PM4 and PM10, and also measures volatile organic compounds. The BME280 handles temperature, pressure and humidity, described as the precision part. And the MIC4514 is the gas sniffer, covering carbon monoxide, ethanol, hydrogen, nitrogen dioxide, ammonia and methane. The readme's framing is that HALO measures everything, and the list supports it. The one thing to notice is the overlap, since three of the four parts report temperature and humidity, which is normal for a node built from accessible modules and is exactly the kind of redundancy you want when the numbers are feeding a display and a notification.

The LED ring is a data channel

The lighting is described as party mode, an eleven LED halo for air quality notifications or for impromptu raves, and the extras section gives it a job, with the ring able to flash when the air quality is bad. That is the feature that makes HALO different from a dashboard you have to open, because a colour on a wall tells you something without a phone in your hand. The hardware detail is specific, since the ring is built from side-fire SK68XX-EC3210F parts, the Adafruit number 4892, running as NEO_GRB with NEO_KHZ800, which is the WS2812 compatible protocol, on GPIO 47. A Bluetooth tracker is also built in, so the device can be used to automate a home or to find keys, and the radio side is described as BLE 5 with BT Mesh alongside the WiFi.

The setup path runs through a captive portal and ends in Home Assistant

The install sequence in the readme is short and the failure modes are the ones you would expect. You power the device with a decent USB-C supply, and the readme warns that a device that reboots repeatedly is usually being starved by a cheap charger. Then you find the access point the device creates, the network named HALO's AP, connect to it from a phone or a computer, and the dashboard appears, and if it does not, the fallback is to type the address directly:

http://192.168.4.1

From there you give the device your WiFi name and password. The Home Assistant path is the same mechanism seen from the other side, adding HALO with ESPHome, accepting the prompts the way you would adopt a device, and assigning it a home area. The readme's own jokes about the wizard are funny once and informative twice, because the flow is a standard ESPHome captive portal, and if you have used ESPHome before you will recognise every step of it.

Calibration and the optional packages are separate documents

Two documents inside the firmware directory carry the detail that a photo cannot. The calibration guide covers CO2 automatic self calibration, the SEN55 heat offsets, a fan cleaning procedure and the NowCast algorithm, which is the weighting the device applies to short term particulate readings. The packages guide covers the optional modular pieces, a BLE stub, offline AQI history, weather and WireGuard. Both are worth reading before the first run, because a sensor node that has not been calibrated produces numbers that look wrong, and a device with no history of its own depends entirely on whatever it is connected to. The self-calibration trick the readme mentions is the other half of that story, taking the device outside so it can calibrate itself against clean air, which is a procedure you can do with any CO2 sensor and which changes the first hours of readings considerably.

The tree shows several hardware variants

The top level of the repository is a set of hardware directories rather than a software project, and that is the clearest signal of how the project is organised. There is a `TFT_LCD/` directory holding the display variant, and the paths quoted in the documentation point into it, with the T-Display-Long version 1 and the ESPHome firmware beneath it. Then there is `No_Screen/`, an `E-Paper/` variant, a `HomeAssistant/` directory, a `components/` directory and a `static/` directory for the web assets. So the same firmware idea is being built in more than one form factor, and a person who wants the simplest possible build should start by finding out which of those directories matches the hardware they have. The project also tracks an image of the first version, and the assets directory carries the branding and the visual material that goes with the device.

Licences, releases and where to ask for help

The licensing is the one detail to read carefully, because the repository carries a file named for the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International licence alongside the main LICENSE.md, and the GitHub metadata records the licence as one it cannot classify. The likely arrangement is that the software is under one set of terms and the CAD and design files under another, with the non-commercial clause applying to the hardware side, which would make sense for an open hardware project that shares the files for personal builds. The releases are numbered by date, with 26.7.25.2 from 2026-07-30 and two from 2026-07-24, and the last push to the repository was on 2026-09-04, so the project is maintained but not at a daily pace. Support is a Discord community, and the readme's framing of it as a hotline is a good description of what a small hardware project can offer. The build instructions are in the wiki, and the author also asks for sponsorship through a coffee page, which is the usual arrangement for a project that has spent real money on boards.

Editorial conclusion

HALO suits a maker who wants their own air quality data instead of a subscription, and it suits somebody who wants a sensor that is visible in a room rather than a box on a shelf, since the ring and the display make the reading part of the space. It is a poor fit if you want a finished product, since you are building the hardware yourself and the documentation is split across a wiki, a calibration guide and a packages guide, and it is a poor fit for commercial redistribution, because the CAD files carry a Creative Commons Attribution-NonCommercial-ShareAlike licence. Before you start, check three things: which sensor board you are buying, since the T-Display-Long-S3 is the design centre of the whole thing, whether you have an ESPHome setup already, since that is what the firmware is, and which licence applies to the part you are using, since the code and the hardware files are not under the same terms.

Frequently asked questions

Official sources

1. Issues
2. README
3. Releases
4. yashmulgaonkar/halo on GitHub