compareeHub

ZSWATCH: BUILD YOUR OWN OPEN-SOURCE SMARTWATCH

A genuinely open smartwatch on Zephyr RTOS — round touchscreen, full sensor suite, and a dev kit with the same chip and sensors while the wrist-sized board is finished.

by Jakob Krantz (jakkra)

FULL CAD BOM FIRMWARE DOCS

ElectronicsWearables

difficulty
●●●●○
time
a serious project
license
GPL-3.0
repo
repo ACTIVE3,374 stars

WHAT YOU’LL NEED

Videos
1
Jump to section

COMPAREE VERDICT

If you want to build and program your own smartwatch firmware on real hardware, ZSWatch is the project. Jakob Krantz open-sourced the whole thing on Zephyr RTOS: firmware, KiCad hardware, and a rich sensor suite (round touchscreen, IMU, pressure, magnetometer, mic, flash). We appreciate the honesty in the docs: the 38 mm watch PCB is marked a prototype, not fully tested, with a clear 'do not order' — the final miniature watch hardware is still being developed. So today the sane path is the WatchDK: the same nRF5340 chip, sensors and display in a larger development board. This is not a beginner build and not a weekend — it's a serious wearables project — and the wrist-sized version is still in progress.

GOOD TO KNOW

  • —Firmware is GPL-3.0; hardware lives in separate KiCad repos
  • —CI (KiBot) auto-generates gerbers/BOM/docs
  • —The bare Watch-HW is marked 'prototype, not fully tested' — the recommended path is the WatchDK dev kit
  • —Chip is the nRF5340 (newer than the old nRF52 versions)

BUILDS OF THE WEEK

Five open-source builds worth your weekend, every week.

Checked like this one: what’s really in the repo, what it costs, how hard it is. One email, unsubscribe anytime.

Can I build this?

Printnothing for the dev kit; watch case files exist for when the wrist-sized board is finalized
Buythe WatchDK dev kit (everything except the battery is included; the battery is optional, it runs off USB-C). The watch PCB itself is not ready to order yet.
Toolsfor the dev kit: minimal; for the bare board: fine SMD rework and ideally factory assembly
Skillsembedded firmware (Zephyr), patience; hand-soldering the board is expert-level
Timea serious multi-weekend project
Costband $$ — current prices: dev kit / parts
Safetylow-voltage; LiPo battery handling care

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

Videos

Building an Open Source Smartwatch Using Zephyr — Jakob Krantz39:51

The creator's Zephyr Dev Summit 2023 talk — the definitive overview.

More builds like this

All projects
Flix: Build a Drone From Scratch on a Cheap ESP32DronesThe Open Book: a DIY E-Reader You Solder YourselfElectronicsSlimeVR: DIY Full-Body VR TrackingVR

Gallery

ZSWatch on the wristZSWatch / jakkra
The v3 caseZSWatch / jakkra
Hardware overviewZSWatch / jakkra
The WatchDK dev kitZSWatch / jakkra

Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the docs (start here)
  2. 2.Watch the creator's talk (40 min overview)
  3. 3.Get the WatchDK dev kit (the recommended path, not hand-soldering)
  4. 4.Build the firmware (Zephyr RTOS)
  5. 5.Join the Discord (the community lives here, not on Reddit)

Resources

Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.

KNOWN ISSUES

  • The 38 mm Watch-HW board is a prototype, not fully tested, and its repo says not to order it yet — use the WatchDK dev kit until it is finalized.
  • It's the nRF5340 now, not the old nRF52 — don't follow outdated instructions
  • Firmware and the KiCad hardware are in separate repos, all under GPL-3.0 — if you fork and share, the changes must stay open.

Can a beginner build this?

Not really. The firmware side is approachable if you know Zephyr, but the hardware is a dense small SMD board. Start with the WatchDK dev kit rather than soldering the bare PCB.

Does it talk to my phone?

Yes — there is an official ZSWatch Companion App on iOS. On Android the companion app is experimental and invite-only, so most people use GadgetBridge.

Which chip is it?

The nRF5340 (u-blox NORA-B10), running Zephyr RTOS. Older versions used the nRF52 — make sure your guide matches your board.

What does it cost?

Band $$ — the dev kit is the simplest way in. Current prices are on the site.

Community builds

No community builds yet — be the first, we feature the best ones.

Discussion1

FROM THE COMPAREE TEAM

The bare ZSWatch board is a dense 38 mm nRF5340 PCB the project itself marks 'prototype, not fully tested' — hand-soldering it is expert territory. Would you attempt the bare board or take the dev kit route?

CompareeTEAM2mo agoedited

Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.

The Open Book: a DIY E-Reader You Solder Yourself

●●●○○ · another wear-it/carry-it open-hardware build, gentler soldering

This open-source handheld turns a tiny Intel NUC mini-PC into a Windows gaming console

●●●○○ · if you like dense DIY electronics you can actually finish

Jakob Krantz (jakkra)

Built a fully open smartwatch on Zephyr and grew a real community and dev kit around it. Funded in part by NLnet/NGI0. Honest about which parts are prototype.

GitHub Web

Star the project on GitHub

DISCLAIMER

  • Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
  • Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
  • Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
GitHub repo