# Why My ESF-551 Scale Kept Disconnecting from Home Assistant: Japan's Measurement Act > Source: > Published: 2026-11-01 05:45:02+00:00 I connected an Etekcity ESF-551, a BLE body scale, to Home Assistant, and not a single measurement arrived. I had Claude Code chase the cause, and it ended at Article 9 of Japan's Measurement Act. Units sold in Japan have the unit switch removed because of that law. I know nothing about firmware or law. What I did was step on the scale and decide what to have it look into next. Without AI, I couldn't have done this investigation. I used the HACS integration `etekcity_fitness_scale_ble`, which wraps `etekcity_esf551_ble==0.8.4`. Claude Code read the log: it showed the integration connecting, reading the HW/SW versions, writing the unit command `a5220305002b0163a10000` (unit 0, kg), and getting disconnected about 0.4 seconds later. Then it reconnected and did it again. No notification ever came when I stepped on the scale, and every sensor stayed `unavailable`. It happened even when the command changed nothing, kg to kg. I left the narrowing down to it too. Claude Code subscribed to `0000fff1` from another machine with plain `bleak` and left out only the unit write. No disconnect. While I stood on the scale, 22-byte notifications arrived about every 45 ms, around 80 of them. So Claude Code wrote a local patch that passes `display_unit=None` and skips the write. All 14 sensors filled in. I had it write the upstream issue too, and filed it ([etekcity_esf551_ble #15](https://github.com/ronnnnnnnnnnnnn/etekcity_esf551_ble/issues/15)). Up to here it was a story about fixing a library bug. I had it look for why only the Japanese version lacks a unit switch. The VeSync app has no unit setting, while the US manual has the steps. Putting the back label next to the US spec showed this was a different market variant, not just a firmware revision. Japanese devices and IoT, again, I thought. | | US ESF-551 | The unit I bought in Japan | |---|---|---| | Capacity | 400 lb / 180 kg | 2–150 kg | | Resolution | 0.05 lb / 0.02 kg | 100 g | | Radio approval | FCC ID 2AB22-ESF551 | Giteki R 210-252428 | | Measurement Act | none | household "正" mark | Claude Code also pulled the Measurement Act from the e-Gov law API and read it. Article 9 forbids selling, or displaying for sale, a measuring instrument marked in non-statutory units. A scale that can show lb or st can't be sold in Japan, so manufacturers drop the unit-switch feature from the Japanese firmware. Weighing myself is neither a transaction nor a certification, so Article 8 doesn't touch the user. Only the seller is bound. The Ministry of Economy, Trade and Industry's FY2015 test-purchase report even has a real case: a vendor who didn't know pounds and stones were prohibited was told to seal the device so it couldn't be switched. What I know is why the Japanese version has no unit switch. I can't tell whether the disconnect itself is intended, or just firmware that doesn't know the command and drops the link sloppily. Removing the feature is fine. I just suspect it was removed carelessly. I only have one unit, so I can't say that model identifier 12 in the manufacturer data marks the Japanese variant. For upstream I suggested registering identifier 12 with `display_unit_settable=False` so the write is skipped, and left the call to the maintainer. An experiment that sends an unknown opcode to see how it disconnects is still undone. The day after I filed the issue, the maintainer replied. That's interesting to know about that Japanese regulation. That would explain it I guess, and since the option doesn't even show up in the app that pretty much confirms it I think. Library v0.8.8 and the HA integration 0.8.3 came out the same day. I updated the integration to 0.8.3, removed my local patch, stepped on the scale, and the measurements came through. That was surprisingly fast, and I'm grateful. Self-hosting Home Assistant is a chore. But it brings lessons like this one, from a bathroom scale all the way to a statute, and I'm glad I do it. *This post was written with AI assistance and reviewed by the author.*