What does HackerNews think of pluto?
Pluto is a programmable digital watch that re-uses case and LCD panel of the Casio® F-91W. (Hardware)
I remember reading about another Casio retrofit:
https://github.com/carrotIndustries/pluto
That version did not have wireless comms - they touch on that in the faq.
I love the new colorways casio recently came out with, I had the plain black for years but now I got myself a pink one as well. The only wrist watch worn by both Obama and Osama!
EDIT: oh wow, googling this a bit there's a different project for a replacement motherboard that already has a compass! I guess I might as well just build one myself. [0]
I doubt that they use any kind of reprogrammable memory, but you can swap out the entire board like I did: https://github.com/carrotIndustries/pluto
But they've made different design decision:
Q: Why is there no accelerometer? A: Accelerometers are the most useful when they're permanently active for applications like sleep trackers, pedometers or features like "shake to do something". Unfortunately, even accelerometers marketed as "ultralow power" draw approx 30 µA when running, draining the CR2016 coin cell in less than half a year. So we decided to dedicate the available space to a digital compass.