This is a SpikenzieLabs Solder : Time™ watch. It uses a a 4-digit 7-segment red LED display that displays the time for about four seconds when the “stem” is pushed in.
There is a CR2032 lithium battery for power, though there is a connection on the circuit board for a power supply. The display could be kept on continuously with a AC/DC power adapter if you wanted to use it as a desk clock (or you could carry around a large battery wired to the watch on your wrist).
The component count is very low – you can see all of them in the photo. The two ICs and the LED module are soldered directly to the board to keep a low profile. The build time for someone familiar with soldering is probably less than an hour. It took me a little longer because I tried to use a yellow LED display module that I ordered from Digi-Key but the digits did not light evenly. The SpikenzieLabs forum suggests that a higher voltage (<5v) might work but I didn’t try it. I unsoldered the yellow module and used the red one.
You should note that this is a big ass watch. A woman’s watch case might be 23-29mm in diameter while a men’s watch case is normally 37-42mm. The Solder : Time case measures ~ 60.8mm (2.4 in). People will notice the Solder : Time on your wrist unless you are the size of Andre the Giant.
The kit sells for $29.95
The new, improved version, the SpikenzieLabs Solder:Time II Watch Kit