I got a
Chipolo wallet card to compliment the Airtags. I posted a pic of it up-thread. As the name implies, it's the size of a credit card (but thicker) and lives in your wallet. Apple things can talk to it, so wallet chipolo is tracked just like other Airtag items.
My experience is that its a bit flaky. Say I'm driving, and stopping at a shop, say, then the post office, I will get an alert "Wallet left behind" often when I start driving again
each time, notwithstanding my wallet has remained in my pocket the whole time (I use the CC linked to my Apple Watch to pay everything on the card). The alerts go to my phone (with me) and are relayed to my watch.
Seems like the Chipolo is sensing movement away from the parked position after it and my phone have been walked around the shop, and hasn't sensed the wallet very near by.
I've tested several times recently and it always gives me an alert if the wallet IS left behind, so it works as intended, but is giving some false positives. The false positives resolved each time by me reaching down and feeling my wallet in my pocket, so not a big thing, but worth noting.