The Device Flasher page is where you load the firmware file you built on the configuration page onto your device. This works for both the T-Watch S3 and the T-Embed, using the same page.

This is called ‘flashing’ the device, as the memory that the firmware is written to is called flash memory.

It all happens in your browser — there’s nothing to install. You’ll need Google Chrome or Microsoft Edge; other browsers such as Firefox and Safari can’t talk to the device over USB and won’t work.

You don’t need any programming knowledge — just work through the page from top to bottom.

Before you start

You’ll need:

• The .bin firmware file you downloaded from the T-Watch-S3 configuration page or the T-Embed configuration page.
• A USB cable that carries data, not just power. Some cables only charge — if your device isn’t found in Step 2 below, try a different cable.
  • The T-Watch S3 uses a USB micro cable.
  • The T-Embed uses a USB-C cable.

Step 1 — Select the firmware file

Under 1. Select Firmware File, click the file box and choose the .bin file you downloaded from the configuration page.

The page checks the file and uploads it. You don’t have to set a start address or any other technical option — the file you download already contains everything the device needs and the page works out where it goes.

If you see an error message here:

• “File must be .bin” — you’ve picked the wrong file, or renamed the firmware so it no longer ends in .bin.
• “File too small” — the file isn’t a firmware image. A real one is at least 0.3 MB. This usually means a download didn’t finish, so download it again from the configuration page.
• “This firmware file is damaged or not from HandShake” — the part of the file that says which device it is for doesn’t make sense. Download it again from the configuration page.

Which device the file is for

Each firmware file says which device it is for. Once the file is uploaded, the page tells you, with a photo: for example “This firmware is for the T-Embed. Plug in your T-Embed.” Check that the device in the photo is the one in front of you.

Older firmware files, downloaded before this check was added in October 2026, don’t say which device they are for. For one of those the page says the file can’t be checked and shows a Continue button instead of the Connect button. Make sure the file is for the device you are about to flash, then click Continue. Downloading the file again from the configuration page gives you one that can be checked.

About the Audio File Status section

Section 2. Audio File Status is there for information only. It lists what it found for both devices, whichever firmware you happen to have selected, so seeing a line about the other device is normal and isn’t a mistake.

You don’t need to do anything in this section. If you chose to have sound on the T-Embed, it is already built into the .bin file — there’s no separate audio file for you to select or flash.

Step 2 — Connect your device

Plug your device into your computer with a data-capable USB cable — micro-USB for the T-Watch S3, USB-C for the T-Embed.

Once the firmware file has been checked, a Connect button will appear under 3. Connect & Flash. Click it. Your browser will show a list of devices — choose the one for your watch or T-Embed and click Connect in that list.

The names in this list come from your computer, not from HandShake, so they’re often unhelpful — something like “USB Serial Device”, “USB JTAG/serial debug unit”, or a string of letters and numbers rather than “T-Watch S3”. If it’s not obvious which entry is your device, close the list, unplug the device, click Connect again and note down what’s in the list without it, then plug the device back in and click Connect once more. The extra entry that appears only when the device is plugged in is the one you want.

If your device doesn’t appear in the list, make sure it’s powered on and properly connected, then try disconnecting and reconnecting the cable.

Step 3 — Install the firmware

Once the device is connected, a small window opens with a few choices. Click Install HandShake code.

You’ll be asked to confirm. There’s also an Erase device tick box — you can leave this alone. The firmware you downloaded is a complete image, so erasing first isn’t needed.

Before writing anything, the flasher checks which device is plugged in. If it matches the firmware you see nothing more. If it doesn’t, it stops and asks you first: see the flasher says this is the wrong device below.

You’ll then see it work through Preparing installation, Writing and finally Installation complete. Writing takes a short while — leave the cable connected and don’t close the browser tab until it says it has finished.

The device restarts on its own once installation is complete, so there’s nothing further for you to do.

Checking which firmware version is on the device

Each time the device starts, it shows a start-up screen for about two seconds before the normal display appears.

The T-Watch S3 shows four lines. Its screen is narrower, so the reset reason has a line of its own:

firmware
2026-10-09d
reset:
power on (1)

The T-Embed shows three:

firmware
2026-10-09b
reset: power on (1)

The date on the second line is the firmware version. The Firmware changes page lists what changed in each version, so you can see whether your device has a particular fix. A letter after the date, such as the d and b above, marks a second or later change made on the same day.

The date is the version of the program, not the day you built or flashed it. A device flashed today can show an earlier date if nothing has changed since then. Each device has its own version, so the watch and the T-Embed can show different dates.

Firmware flashed before 9 October 2026 doesn’t show a start-up screen. Build and flash new firmware to get it.

What the reset line means

The reset line says why the device started. The number in brackets is the code the chip itself recorded. The watch shows the same messages, split over two lines, so reset: power on (1) below appears on the watch as reset: with power on (1) underneath.

A watch whose version is earlier than 2026-10-09d shows the version but no reset line. Build and flash new firmware to get it.

If the start-up screen appears more than once before the normal display, the device restarted each time and the reset line shows why the last restart happened. When you get in touch about any problem, please include the whole start-up screen: the version and the reset line.

If something goes wrong

Don’t panic. If flashing fails partway through, or you flash the wrong file by mistake, just reconnect the device and repeat the steps above with the correct file. There’s no way to damage the device by flashing it again.

The flasher says this is the wrong device

The firmware file is for one device but the other one is plugged in: for example a T-Embed file with a T-Watch S3 plugged in. Either you picked the other device’s file or you plugged in the other device. The flasher stops before writing anything and shows photos of both devices.

• To fix it, click Cancel. Nothing is written to the device and it carries on working as before. Then either plug in the device the file is for, or select the file for the device that is plugged in. Each configuration page downloads the file for its own device.
• Flashing anyway is possible: tick “I understand…”, then click Flash anyway. Nothing will be damaged, but the device’s screen will stay black and it won’t work until you flash it again with its own firmware. That fixes it completely: the flasher always recognises the device itself, whatever firmware is on it.

The flasher could not tell which device this is

The flasher reads the device to find out what it is, and this time it couldn’t tell. It shows a photo of the device the firmware is for. If that is the device plugged in, click Continue and it flashes as normal. If not, click Cancel: nothing is written. Please let me know if you see this message with the right device plugged in, as it means a new batch of devices reads differently.

Other problems

• Device not detected? Check it’s connected and powered on. Try a different USB cable or a different USB port on your computer.
• Flash failed? Disconnect and reconnect the device, then try again.
• Still stuck? Open the browser’s developer console (press F12) to see if there’s an error message and get in touch if you need help — it’s useful for me to know if you’ve hit a problem.

T-Embed repeatedly not detected

Once the watch has been shaken, the T-Embed becomes a keyboard and the Device Flasher can no longer find it. Unplug the T-Embed, plug it back in and click Connect before shaking the watch, or switch the watch off first. If it is still not detected:

• Unplug the T-Embed from the USB cable.
• Push in the button in the middle of the jog dial.
• Keep this button pressed while you plug the USB cable back in.
• Release the button. The display will probably stay black.
• Now the T-Embed should be detected and flash.

T-Watch repeatedly not detected

• Have a look at the section ‘Resetting the watch if it becomes unresponsive’ in this page: watch_configuration_help