Open-Source Smartwatches & Wearables

A small but vibrant scene of fully open-source wearables: open hardware schematics, swappable firmware, hackable on a Tuesday night. None of these are as polished as an Apple Watch or as accurate as a Garmin — but you own them down to the silicon.

Sister sections: Apple Watch, Garmin, Oura & Whoop, GadgetBridge & Aggregation, MCU Platforms, Embedded Rust, BLE & Bluetooth IoT, Quantified Self DIY.

PineTime (PINE64)

• ★ PINE64 PineTime — open hardware NRF52832-based smartwatch; ~$30 retail; HR, accelerometer, color LCD, BLE; community-developed.
  • https://www.pine64.org/pinetime/
• ★ InfiniTime — the dominant FOSS firmware for PineTime; FreeRTOS-based; activity counts, HR, notifications, music control; Watchface SDK; OTA via GadgetBridge / nRF Connect / amazfish.
  • https://github.com/InfiniTimeOrg/InfiniTime
• Wasp-OS — alt MicroPython firmware for PineTime; smaller community; useful if you'd rather Python than C++.

The PineTime is the gateway open-source smartwatch in 2026 — it's cheap enough that bricking it is fine and the community is large enough to ask questions.

Bangle.js 2

• ★ Bangle.js 2 (Espruino) — open hardware + open firmware; JavaScript on your wrist; nRF52840; HR, accel, vibration, GPS bandable; ~$80.
  • https://www.espruino.com/Bangle.js2
• App loader — install / write apps from the Web Bluetooth IDE; a few hundred community apps and watch faces.
• The "I'd like to write my own watch app on the toilet on a phone" choice. Genuinely fun.

Watchy (SQFMI)

• ★ Watchy — ESP32-based Arduino smartwatch; e-paper display; week-long battery; ~$80 kit. Hardware design is open; you 3D-print the case.
  • https://watchy.sqfmi.com/
• PlatformIO + Arduino dev flow. See Arduino & PlatformIO.
• Crystalfontz / open watch face repos — community face library.

The Watchy is the maker's smartwatch — barebones, ugly by default, fully programmable. Good companion to ESPHome + Home Assistant.

AsteroidOS

• ★ AsteroidOS — FOSS Linux-based smartwatch OS; replaces Wear OS on a number of Wear OS-era hardware (Asus ZenWatch 3, LG Urbane, Sony SmartWatch 3, Mobvoi TicWatch E2/Pro, others).
  • https://asteroidos.org/
• Active dev; Bluetooth pairing with Android via asteroid-companion.
• Niche but the right answer if you have aging Wear OS hardware lying around.

RP2040 / Pico-based watches

• WatchX, OpenWatch, MiraOS — DIY watch projects on RP2040 or nRF52; lower polish but hackable.
• Adafruit Feather + LCD + battery — DIY scaffolding. Genuinely a weekend project.

Mi Band / Amazfit + GadgetBridge

• ★ GadgetBridge — FOSS Android client; pairs with Mi Band 4/5/6/7/8, Amazfit GTR/GTS/Bip, Fossil Hybrid, Sony SmartWatch, Pebble, and Pixel Watch (limited). Reads steps, sleep, HR, notifications — without the official app or cloud account.
  • See GadgetBridge & Aggregation.
• The closest thing to "open-source firmware on closed hardware" — you don't reflash, but you replace the cloud account with a local app.

Pebble revival

• Rebble — community keeping classic Pebble watches alive after Fitbit shut it down; firmware updates, app store, weather; works on Pebble Time / Time 2 / Time Steel.
  • https://rebble.io/
• ★ Core Devices Pebble 2 successor (announced 2024 by Eric Migicovsky) — small batches; runs PebbleOS open-sourced by Google in early 2025. Worth tracking in 2026.

CrowPanel / TrueWear / Hexabyte

• CrowPanel — Elecrow's ESP32-S3 + 1.4" round screen kits; effectively a Watchy with a color screen.
• DIY Arduino smartwatch tutorials — ample on Hackaday / Adafruit; for the "I want to learn embedded" crowd.

Sensor / firmware ecosystem

• Open BLE HR strap firmware (community ports of Polar H10-style firmware to nRF52 dev kits) — niche but exists.
• See Embedded Rust and MicroPython / CircuitPython for firmware language choices.

Reality check

• ★ None of these match Apple Watch / Garmin sensor accuracy for HR / HRV / GPS. They're for hobbyists, not endurance athletes.
• Battery life is generally good (e-paper Watchy = days; PineTime / Bangle.js 2 = days).
• App ecosystem is thin — no Strava on your Bangle.js. (You can sync via GadgetBridge but features are limited.)
• The point is ownership, learning, and modification — not parity with the closed flagships.

Cost / license honesty

• PineTime — ~$30 hardware; InfiniTime / Wasp-OS GPL.
• Bangle.js 2 — ~$80 hardware; firmware MIT/Espruino-licensed.
• Watchy — ~$80 kit; firmware MIT.
• AsteroidOS — repurpose old Wear OS hardware ($0-50 secondhand); GPL.

Pick this if…

• Cheapest "real" open watch: PineTime + InfiniTime.
• JavaScript on your wrist: Bangle.js 2.
• E-paper, Arduino, hackable: Watchy.
• Repurposing old Wear OS: AsteroidOS.
• Closed hardware, open client: Mi Band / Amazfit + GadgetBridge.
• Pebble nostalgia: Rebble + watch out for the 2026 Core Devices Pebble.
• Want sensor accuracy + polish: none of these — see Garmin or Apple Watch.