DATA-2000 was released by Seiko (Hattori Seiko and Seiko Electronic Industries) in 1984.
The world's first wrist computer, commonly known as the "arm computer".
This model can be said to be the originator of current smartwatches such as the Apple Watch.

This model is an export model for the United States, and unlike the "UC-2000" for Japan, it is a rare model with a black main body, belt, and keyboard.
In addition, in the domestic specification, the watch body is labeled as "UC-2000" and the keyboard is labeled as "UC-2100," but this model's watch body and keyboard are both labeled as "DATA-2000."
The model numbers of DATA-2000 are: wristwatch: UW01-0020, keyboard: UK01-0030.

By setting the watch body to the keyboard and switching to "TRANSMIT" mode, characters entered on the keyboard can be transferred to the watch body.
The watch itself also serves as a display during keyboard input.
Memo function (1000 characters x 2) and calculation function can be used using the display section (dot matrix 10 characters x 4 lines).
Its specs were overwhelmingly poor compared to today's computers, but at the time, being able to connect a wristwatch to a keyboard and enter notes was groundbreaking in itself.
In Japan, the UC-2000 series has a system that says, "Today I'm learning English words, but yesterday I had a game installed."My “Arm Con” is newly released on Earth.It is being sold with a rather catchy catchphrase.

As I wrote in the caption of the back cover photo, there is actually no contact terminal for data transfer between the DATA-2000 watch body and the keyboard, and a wireless transfer method is used.
Both the watch itself and the keyboard contain coils that create electromagnetic induction to transfer data.
The metal part you see above the part of the keyboard where the watch body fits (the "TRANSMISSION CIRCUIT" part in the photo) is simply a spring that holds the watch in the correct position when inserted.

The coil on the watch side is exposed on the outside of the coin battery when you open the back cover, and if the coil is damaged or disconnected, communication will no longer be possible, so replacing the battery on this model can be quite stressful.

In addition, the screen display density of this model is very dark after battery replacement, so it is necessary to adjust the screen display density using the keyboard.
Immediately after replacing the batteries with new ones, the condition will be as shown in the photo on the left below (maximum density), so unless you adjust the density, you will not be able to read the text properly...

By the way, to adjust the density, press the "CNT▲ (Contrast)" key on the keyboard to make it dimmer, and "SFT (Shift)" + "CNT▲" keys to make it lighter.
Occasionally, only the watch itself is put up for sale at online auctions, but since the concentration cannot be adjusted with just the watch, it may be virtually useless if you don't have a keyboard.
Maybe it will work if I put in a weak battery.