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 an LCD screen displays what is in each box by 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 surfaces) and also 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 stickers) 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 thought of making something simple to learn more about it.