TECH

Round smartwatch with Bosch gas sensor and open-source software launches 2027

Next year, the Bangle.js 3 will hit the market as a brand-new smartwatch that combines a round color display with an open-source operating system and a modern design. The manufacturer has now confirmed the key specifications in advance.

The Bangle.js 2 from 2021 is finally getting a successor with a much more modern look. The team behind the open-source smartwatch has published images and extensive details about the Bangle.js 3's specifications ahead of its expected launch in summer 2027, although pricing details have yet to be announced.

The predecessor's small, rectangular display is being replaced by a round display with much thinner bezels, using a 1.2-inch LCD with a resolution of 240 x 240 pixels that can display 64 colors. Combined with a metal bezel, this makes the watch look significantly more modern than the Bangle.js 2. The watch features speakers, microphones, a vibration motor and a heart rate sensor.

The screen measures 1.2 inches across at 240 by 240, putting out 64 colors. It renders into a square frame buffer, so the corners of that buffer simply aren’t visible on the round panel. Williams sized the case to take the same straps as the Bangle.js 2 and to sit at the same height on the wrist. The new case runs slightly thicker and wider than the old one, though

One sensor stands out from the spec list. Bosch’s BME690 is a smart gas sensor that can fingerprint specific smells, detecting gases in the air around the watch, and no mainstream smartwatch offers anything like it.

Williams flags the catch himself, though: sourcing that sensor at a sensible price is still an open question this far out. He’s spent the whole project adding features without letting the price jump, and this is the one line item still fighting him

Nothing on the case is glued. The rear cover unscrews, and inside sit test points placed there so owners can bolt on custom hardware of their own. Williams also plans to release the CAD files for a deeper back, an open invitation for someone to print a case back with room for a much bigger battery.

A four-pin connector hides behind the top strap. It handles charging, SWD programming and debug UART output, plus two analog-capable GPIO pins and a switched 3-volt output. For a watch, that’s an unusual amount of access, and it’s there on purpose. It’s, in effect, a tiny bench supply and debug header riding under the strap

A Nordic nRF54L15 runs the watch, an Arm Cortex-M33 ticking at 128 MHz, with Bluetooth LE handling the phone link. Wi-Fi arrives through a separate ESP32-C2 chip at 2.4 GHz, and that chip can even turn its hand to 2.4 GHz SDR work. Storage is 32 MB of flash memory.

The sensor stack runs long: an accelerometer, a gyroscope and a magnetometer track motion, a barometer and an air temperature sensor watch the weather, and a heart rate sensor covers the wearer. Add a speaker, a microphone and a vibration motor. Then add a torch, an RGB indicator LED, and an infrared transmitter and receiver that can work a TV remote’s job.

While more advanced health sensors, a GPS module and an NFC chip are missing, the watch offers a Bosch gas sensor designed to detect certain smells. An LED flashlight is also said to be on board. The roughly 200 mAh battery is charged wirelessly. One distinctive feature of the Bangle.js 3 is that the watch uses an open-source operating system, allowing the community to expand its functionality.

In keeping with this, the case can be easily opened with a few screws, while four pins on the case provide both power and data connections for diagnostic and programming purposes. With an ARM Cortex M33 (nRF54L15) processor with clock speeds of up to 128 MHz, Bluetooth Low Energy and only 32 MB of memory, the smartwatch is not particularly powerful, but should offer relatively long battery life.

Display	1.2-inch round, 240 x 240, 64 colors
Processor	Nordic nRF54L15, Arm Cortex-M33 at 128 MHz
Wireless	Bluetooth LE, 2.4 GHz Wi-Fi via ESP32-C2
Memory	32 MB flash
Buttons	4 (1 left, 3 right)
Bezel	Metal front bezel
Sensors	Accelerometer, gyro, magnetometer, barometer, air temperature, heart rate
Gas sensor	Bosch BME690, not confirmed for the base model
Battery	Around 200 mAh, wireless charging
Case	Unscrewable rear cover, internal test points
Connector	4-pin: charging, SWD programming, debug UART, 2 analog GPIO, switched 3V output
Extras	Speaker, microphone, vibration motor, torch, RGB LED, infrared transmitter and receiver
Straps	Same straps as the Bangle.js 2
Availability	Summer 2027, expected

Compatibility work is already underway. Existing Bangle.js 2 apps are being brought across to the round screen, and widgets currently draw inside a square while the port settles. Most apps should just work once they’ve been updated for the round layout.

That’s the deal with this line: the  watches run Espruino, open-source software, and the app library owners have built up around the square  watch is the library the round one inherits. Keeping that library alive is a design goal here, not an afterthought.

An email signup is open now for anyone who wants an alert the day the watch goes on sale

Battery capacity lands around 200 mAh. That’s much the same as the current watch, and charging is wireless. Rain and hand washing are fine, per Williams. Swimming isn’t advised, and there’s no water resistance rating to quote, because he hasn’t published one.

Expect the watch in summer 2027, if the current plan holds. A pre-order is likely, but only once Williams has mostly final pre-production units in hand and trusts the timescales. Pricing isn’t set yet, and neither is the final sensor list. The one guide he’s offered is that it’ll land a little above the current model’s price.

mundophone