I have never looked into it myself (if the question was for me), because it (the "making a ring out of a keycard chip thing) was never something I was interested in. My phone works for me, and although I have an apple watch, I have not missed not having a way to open the car with my watch.
I know there are solutions but havent investigated it myself, sorry.
Yeah, I meant anyone on the forum. Do want to be stuck with a $100+ mistake if it doesn't work.
here's a few https://www.teslaring.com/
https://www.amazon.com/COLMO-Accessory-Replacement-Customization-Worldwide/dp/B083F2N8NM
Main thing would be waterproof for swim etc.