A round screen is the headline change for the Bangle.js 3. Gordon Williams, the man behind the open-source Espruino watches, has published a hardware update on the next model, and the square face that defined the first two generations is gone. In its place sits a 1.2-inch round display with a metal bezel around it.
Hardware is mostly nailed down, in Williams’s words, with CAD designs finished and a development board already running apps. This is the third generation of a watch line built on a simple idea: the software is open, the case opens, and owners can tinker with both. Nothing here is sealed shut.
Bangle.js 3
Round 1.2-inch 240 x 240 screen · Nordic nRF54L15 chip · Open-source Espruino software
Price: TBD, expected summer 2027
Where to buy: More details at Espruino
Round face, same straps
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, though the new case runs slightly thicker and wider than the old one.
Four buttons ring the case this time, one on the left and three on the right, and the front bezel is metal.
A nose for the watch, if the parts cooperate
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.
If the numbers don’t work, the base watch ships without it. A Pro variant carries the sensor instead.
Built to come apart
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.
New silicon, and Wi-Fi joins the spec sheet
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.
It’s a lot of hardware for a watch this open.
| 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 |
Your old apps come along
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.
Bangle.js 3
Unscrewable rear case with test points inside · Wireless charging · Bosch gas sensor still to be confirmed
Price: TBD, expected summer 2027
Where to buy: More details at Espruino
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.
