For anyone interested in modding the F-91W there's also The Ollee Watch, a replacement PCB which adds even more "smart" features.
https://www.olleewatch.com/
The developer also recently posted on Reddit that he’ll soon be adding third party app support
Sensor Watch is the non-phone-connected OG:
https://www.sensorwatch.net
The developer also recently posted on Reddit that he’ll soon be adding third party app support