Hacking with Claude on a $27 smart watch

TL;DR Highlight

Built a custom watch face for a $27 PineTime in hours using coding agents

Who Should Read

A backend or app developer who wants to try coding agents on embedded or hobby hardware

Core Mechanics

Open firmware and a simulator suit agents
- The PineTime costs $27, runs open source InfiniTime firmware, and is well documented.
- The InfiniSim simulator gives the agent a fast feedback loop on the computer.
Most work was done in OpenCode with open-weight models
- The post keeps saying "Claude" but most work happened in OpenCode.
- Models used were Kimi K3, K2.6, and DeepSeek v4 Pro and Flash.
First attempt from a photo was rough
- The agent was given a Casio watch face photo and an existing InfiniTime watch face as a base.
- It guessed text sizes and positions, so elements overlapped and were unreadable.
Fixed one element at a time
- To save tokens, the author gave isolated tasks and concrete next steps.
- Each text element was finished before moving to the next.
Static parts became a fullscreen background image

Community Reactions

Opinion that PineTime's RAM is a painful bottleneck
- A reply says the upcoming "pro" version may fix this and links a Pine64 post.
Experiences hacking other devices with AI
- One commenter built a random I-ching "kookwatch" on a lilygo t-watch with Codex.
- Others built a Garmin calorie tracker with Claude and revived a 10-year-old Pebble watch face.
Complaint that the "Claude" naming is confusing
- A commenter found it misleading that the post says Claude throughout despite using other models.
- Another asked whether Claude is becoming the Kleenex of agents.
Info that PineTime has no microphone
- So voice control is impossible.
- Several commenters asked for other hackable watches, and one suggested the Waveshare ESP32-S3 AMOLED 2.09” watch.

How to Apply

Have your agent get InfiniSim building today
- Clone the InfiniSim repo and ask the agent to get a build working.
- Once the simulator runs, you can experiment without owning a PineTime.
Give the agent a screenshot feedback loop
- For UI work, let the agent see simulator screenshots directly.
- This cuts manual description and token use.
Split big tasks into one element at a time
- Give concrete next steps for a single element.
- Move on only after it is right.
Have the agent write lessons into AGENTS.md
- At the end of a session, ask it to summarize problems and fixes into AGENTS.md.
- The next session or another person avoids the same pitfalls.

Try It

copy & run

# Paste into Claude Code or OpenCode as-is (the article's method turned into a prompt)

Clone the InfiniSim repo (with the InfiniTime submodule) into {{work folder}} and get it building in this environment.

Once it builds, use an existing watch face as a base to make a watch face similar to {{reference image}}.
Feel free to use sub-agents for well-scoped tasks.

Fix only one text element at a time, and move on to the next after I confirm.

At the end, summarize what you learned and what blocked you in AGENTS.md.

Terminology

InfiniTimeOpen source firmware that runs on the PineTime. Think of it as the watch's OS.

InfiniSimA simulator that runs InfiniTime on your computer. A test environment that lets you see results without a real watch.

OpenCodeA coding agent tool that can plug in various models. The author used it instead of Claude.

AGENTS.mdA project guide file that agents read. Like a handover doc for a new hire.

Watch faceThe visual design of a smartwatch's clock screen.