[xdavidhu]

I wish there were a way to put the chip & antenna inside (or behind?) the watch casing.

While this is really impressive, putting something in front of the faceplate breaks the great F-91W look and feel for me.

[jqpabc123]

Or just forget the watch and casing and build an add-on to the strap to hold the NFC chip. This should work with any watch strap that isn't metal.

Similar project I did to carry a microSD memory card.

https://www.thingiverse.com/thing:6784665

[jonhohle]

Projects like ollee Watch seem to be able to stash it behind the front crystal or underneath the LCD.

[xdavidhu]

Ollee does that by replacing the original PCB. In this project the movement is kept original.

I recall the blog n-o-d-e did successfully put an NFC chip inside while also retaining the default PCB, so there is at least some free space in the case...

https://n-o-d-e.net/casio.html (0:56)