I saw a TimexPay watch band that says it can be connected to any Chase Visa credit or debit card for contactless, so I ordered it ($40)
The package contains the watchband, some sort of clip, and a micro USB cable.
I found that the band piece with the buckle contains the active element.
The clippy thing has an FCC IDD.
FCCID lookup: FCC ID 2AVQ70072-UPPU
There is nothing visible inside the clip.
The instruction card says the clip requires power when setting up the RFID, so I’m guessing it programs the chip using a Bluetooth connection to the phone.
I cut the thread and pulled on the thin leather face. The edges of the band appear to be coated in rubber.
The active element inside. Held with a small amount of double sided tape. There’s some reinforcement on this side since all the chip to coil connections are on this spot.
The side with the flip chip.
Size is ~11x26mm.
Scanning it on Android shows an Infineon Unknown IC using ISO/IEC 1443-4 and Gemalto card manager.
That’s all I got. This seems to be as small or smaller than the available contactless options for custom conversion. I don’t have a particular want for conversion, but I thought it’d be fun to tear down and share.