The Sensor Watch circuit board [1] inside the case of a Casio F91-W / A158W / A159W satisfies 2, 4, 5, and 6. Accelerometer or thermometer available as daughterboard. Battery life measured in months, if not years. Although the simple LED backlight and the segmented LCD leaves a bit to be desired, and there is no wireless connectivity for notifications. Open source firmware.
The Ollee watch circuit board [2] is similar, better backlight but closed-source firmware and configuration over BLE in a smartphone app. Still no notifications over BLE though.
I'd think combining 1 and 6 (O₂ monitoring and waterproofing) would be difficult.
> I'd think combining 1 and 6 (O₂ monitoring and waterproofing) would be difficult.
By O2 monitoring, they mean "blood oxygen through skin via LEDs" - there's no impact on waterproofing from that (as the Apple Watch demonstrates.)
The Pro version has a better screen (still segmented but more), RGB LEDs and an infrared sensor.
my experience with a sensor watch has been terrible.
imagine breaking a $3 watch that is not quite as indestructible as people think it is, but it is nonetheless pretty robust, and then trying to shove something 100x glitchier and 5x as expensive into its case...