You are reading a single comment by @user140377 and its replies. Click here to read the full conversation.
Well, this could also be done over BLE. what type of sensor is worth the hassle of wiring it to the watch and wearing such combined result on your wrist? puckjs or any cheap nrf52 module running espruino can do such BLE to i2c/spi/serial bridge and you can have the sensor in a pocket or other suitable location
With inspiration from https://github.com/joeycastillo/Sensor-Watch: Route i2c to the additional pins of the watch so we can attach external sensors.