SQFMI has designed a (mostly) open-source hardware smartwatch based on an ESP32-S wireless module for WiFI and Bluetooth connectivity, and equipped with an E-ink display of 200x200 resolution.
Watchy also comes with a BMA423 accelerometer, four buttons, a DS3231 real-time clock, and a vibration motor. The watch should last around 2 weeks on a charge.
I mentioned the watch is "mostly" open source hardware because while the GERBER files, bill of materials (BoM) and the PDF schematics have been released on Github, the KiCAD schematics and PCB layout files have not so far. That still means you can