125khz RFID Writable rewritable T5577 fob tag for RFID Writer (Pack of 10) (Black) https://a.co/d/7oo01qa
This is the exact same chip already in a keyfob, or you can put one of these small stickers inside
YARONGTECH 125khz rewritable T5577 Sticker Coin Adhesive Back Dia 25mm Thickness 1mm (5) https://a.co/d/2nMXbyH