Cobalt

Cobalt Lab

What we are working on.

We are two engineers and we are building in public a board for the F-91W digital watch. This page gathers the questions we are working on, what we will publish, and how to work with us.

Our research areasWork with us
V1Prototype boards, worn every day since September 2026.In use
V2The board of the campaign. It fixes what the V1 taught us.In design
14.7 µA

average consumption

Estimate
5 months

of battery life on a 60 mAh coin cell

Estimate
850 ms

to reconnect to the phone

Measured on the V1
5 µAh

per 3-second voice command

Estimate
4 s

from the voice to the action on the phone

Measured on one note

Our research areas

Where we think we can move research forward.

Area 01

Zephyr: very low power

Lasting months on a coin cell with a radio and a microphone: what we learn, proposed upstream to the Zephyr project.

Where we are
The firmware runs under Zephyr on the V1 boards. According to the datasheets, the watch draws 14.7 µA on average, of which 10 µA in standby. No current has been measured yet: we don’t have the instrument.
What we will publish
The measurement method, the raw traces and the energy model. On the Zephyr side, a driver for the BMA400 accelerometer, with its low-power mode and its wake-ups.
Zephyr pull request
Not opened yet.
Area 02

Zephyr: an LCD driver

The driver of the watch’s segment display (ROHM BU97930), proposed to the Zephyr project.

Where we are
The driver runs the original display on the V1 boards, except the tens digit of the hours. Its code is in the firmware repository.
What we will publish
A BU97930 driver for Zephyr’s auxdisplay subsystem.
Zephyr pull request
Not opened yet.
Area 03

Cobalt Link

The open protocol between the watch and the phone.

Where we are
The test vectors are published. The specification is still to be written.
What we will publish
A public specification of the protocol, with its test vectors.
Area 04

The agent on the phone

A voice agent that acts in the phone’s apps, locally or in France.

Where we are
The app reads the common commands on the phone, with no network: timer, alarm, reminder, appointment, music, directions. For freer requests, a Mistral model proposes an action, which only starts with your agreement. This second mode is on trial with us and with a few testers.
What we will publish
The rules that decide what the agent can start, and their tests.
Link
Content missing

The open programme

What we open, piece by piece.

What we openStatus on 6 October 2026
The firmware of the watch, under Apache-2.0Publishedsince 30 September
The V2 board: KiCad sources, EasyEDA and Altium versions, manufacturing filesTo be drawnlicence still to be chosen
Cobalt Link: a public specification of the protocol, with its test vectorsIn partthe vectors are published, the specification is still to be written
The watch in Gadgetbridge, the free Android app that asks for no accountTo do
Activity at the lowest current: detectors and dataTo do
A security review, publishedTo do
Drivers and the board definition in ZephyrTo do
A royalty-free codec, negotiated by the protocolTo do
The owner’s firmware over the wireless link, and an open rescue adapterDecidedfor the V2
An illustrated guide to fit the board in an F-91WFirst versionon the Builders page

Work with us

Tell us what you have in mind.

Write to us

Laboratories

What we offer: boards, data, and a real product to test a method on. We co-sign what gets published.

What we are looking for: a precise current measurement, because we don’t have the instrument, and people who know speech, activity recognition, security, or how people interact with an agent.

Schools and students

What we offer: final-year projects and R&D internships on the subjects of this page.

What we are looking for: students who are curious about very low power.

PhD students

What we offer: a CIFRE thesis, later.

What we are looking for: a laboratory ready to carry the subject with us, when the time comes.

Security researchers

What we offer: a disclosure policy, public thanks, and a watch to attack.

What we are looking for: a report in private, at jean@cobalt-watch.com. See the security page.

Be told as soon as Cobalt is available.

We only use your address to tell you. Privacy policy

Legal notice

Publisher

Cobalt Watch, a French simplified joint-stock company (SAS) with a share capital of Content missing euros.
Registered office: Content missing, Paris 2e, France.
Paris Trade and Companies Register (RCS): 106 218 159.
VAT number: Content missing.
E-mail: jean@cobalt-watch.com
Telephone: Content missing

Publication director

Jean de Bailliencourt, president of Cobalt Watch.

Host

Hostinger International Limited
61 Lordou Vironos Street, 6023 Larnaca, Cyprus
hostinger.com/contact

Other names

Cobalt Watch and CB-91AI are the names of our company and of our board.

The other company and product names on this site belong to their owners. We name them to say what our board and our app work with, or to compare them with our products.

Licences

The firmware of the watch is published under the Apache-2.0 licence.

The other texts, the photos, the videos and the logo belong to Cobalt Watch. For any other use, ask us.

Credits

Typefaces: Hanken Grotesk, Martian Mono, Instrument Serif and IBM Plex Sans, under the SIL Open Font License. Photos and videos: Cobalt Watch.

The Android robot is reproduced or modified from work created and shared by Google and used according to terms described in the Creative Commons 3.0 Attribution License.

Accuracy

We do our best to keep this site accurate and up to date. It can still contain a mistake, and we change it as the project moves. If you spot one, tell us.

Applicable law

This site is governed by French law.

Privacy policy

This site sets no cookie and loads nothing from other companies: no analytics, no advertising, no embedded video. So there is no consent banner. Here is the little we do handle.

Who is responsible

Cobalt Watch SAS, the company that publishes this site. For any question about your data, write to jean@cobalt-watch.com.

What we handle

WhatWhyHow longWhere
The e-mails you send usTo answer you. We have a legitimate interest in doing so.Content missingOur mailboxes, at Hostinger
Your e-mail address, if you subscribed to our newsTo send you the news you asked for. This rests on your consent.Until you unsubscribeBrevo, our mailing provider, in France
The server’s logs: IP address, date, page requested, browserTo keep the site running and secure. We have a legitimate interest in doing so.Content missingHostinger, our host
Your name and your e-mail address, if you join the waitlistTo tell you when the campaign opens, and to contact you if you asked to test. This rests on your consent.Until you ask us to remove you, or Content missingA Google spreadsheet, filled by a Google Apps Script

Content missing

Who receives it

Hostinger, which hosts the site and our mailboxes, Brevo, which sends our news, and Google, which keeps the waitlist. We don’t sell your data and we don’t pass it to anyone else.

In your browser

If you switch language with the FR / EN button, your browser remembers that choice so that you get the same language next time. This choice stays in your browser and is never sent to us. Nothing else is stored there.

Your rights

You can ask us for a copy of your data, have it corrected or deleted, object to its use, and withdraw your consent at any time. Write to jean@cobalt-watch.com: we answer within a month.

If you think we handle your data badly, you can lodge a complaint with the CNIL, the French data protection authority.

The app

The Cobalt Agent app has its own privacy policy, because it handles something else: your voice notes. It is on its own page.

Notice about Casio

We are independent. Cobalt Watch is not affiliated with Casio Computer Co., Ltd. or with any of its subsidiaries. Casio has not endorsed or sponsored our products or this website.

The names. “Casio” and “F-91W” are trademarks of Casio Computer Co., Ltd. We use them for one reason only: to say which watch the CB-91AI board is made for. When a Casio watch appears in a photo or a video on this site, it is there to show that compatibility.

What we make. The CB-91AI is an electronic board that we design ourselves. It replaces the board of a watch that you already own. We don’t make the watch, and we don’t sell Casio watches.

Modifying your watch. Fitting the board means opening and modifying your watch. You do it at your own risk. It ends the manufacturer’s warranty on that watch, and we can’t be held responsible for damage done to it while fitting the board.