The Casio F-91W has somewhat of a cult following because of its cheap and robust design, and legendary 7 year battery life.
Having gotten used to NFC payments from my Apple Watch, I wanted to see if I could mod my Casio to do the same.
My bank offers these Gemalto stickers, shrunk down versions of a normal credit card and without the magstripe or the chip, just the contactless coil. They were originally launched before Apple Pay and Google Pay arrived in New Zealand as a poor man's mobile payment alternative.
After submerging the card in acetone for about an hour, the plastic dissolved, leaving the NFC coil and IC exposed. With a bit of care and cleaning, I rewound the coil to fit inside the body of the watch, glued it in place, and repacked it all together.