Claude Code Lego Flag Hook
Description
Lego mailbox with a servo-driven flag that goes up when Claude Code finishes responding and down when you send a new prompt. Driven by Claude Code hooks.
Installation
This entry records only its repository, not the path inside it, so there is no
exact command to give. Open the source below and copy the folder into
~/.claude/skills/, or the file into ~/.claude/agents/.
README
Claude Code Lego Flag
A physical Lego mailbox with a motorised flag that tells you when Claude Code is working vs. ready for your next prompt. A servo raises the flag when Claude finishes a response and lowers it as soon as you send a new message.
It's a tiny ambient signal you can see from the corner of your eye — no terminal bells, no polling your screen.
[](https://www.youtube.com/watch?v=u6cx7Jbch5Y)
How it feels
| State | Flag | Trigger |
|---|---|---|
| Claude thinking | down | Claude Code UserPromptSubmit hook fires on your input |
| Claude idle | up | Claude Code Stop / SessionEnd hook fires |
A third command, `W` (wave), raises the flag for 1.5 s and drops it again — handy for notifications or testing.
Bill of materials
| Part | Notes |
|---|---|
| RF-Nano V3.0 | Arduino Nano clone with integrated NRF24L01 + CH340 USB-serial. Sold in Micro-USB and USB-C variants — any works. |
| Geekservo 270° | 3–5 V programmable servo with Lego-compatible horn. |
| Dupont M-M jumpers | Or solder directly to the Nano (see note below). |
| Lego bricks + flag piece | Any small mailbox-style build that fits a 2x2 servo and a flag. |
| USB cable | Match the Nano variant (Micro-USB or USB-C). |
On macOS the CH340 is recognised by the built-in `AppleUSBCHCOM` driver — no install needed. The port appears as `/dev/cu.usbserial-*`.
Lego model
I designed the mailbox myself in [Mecabricks](https://mecabricks.com/en/workshop/0DvYleNWj9e) before buying any bricks, so the build was known to fit arou
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