Hello r/watchrepair community

I recently came across my late grandfather's analog watch, which has a unique design. It's an analog watch, yet it contains a motherboard. Intriguingly, the hands of the watch are still functioning correctly even though the battery is disconnected. There's also an unusual opening on the side of the watch. I'm curious if anyone in this community has ever seen or heard of a watch like this. I'm including pictures for better understanding. Any insights or information would be greatly appreciated!"