I am working on a project where I have 3 boxes and a RFID reader (mfrc522) attached at the bottom of each box. I keep my wallet/keys/etc in these boxes and a LCD screen displays what is in each box via reading the rfid tag on the wallet/keys/etc. But sometimes it has trouble detecting my keys which I assume is due to other RFID tags and keys (metal surface) as well as it simply won't detect my phone or other electronic devices. Hence, I am looking for an alternative to RFID that I can use to monitor the stuff in these boxes. I need the tags to be super thin (for RFID I was using RFID sticker)so that I can attach the tags to anything.
PS- This is just for an educational project. I am relatively new to item tracking systems and though of making something simple to learn more about it.