If you have the passport card, it’s probably a good idea to keep it in the little foil RFID shield sleeve which comes along with it.
The new passports (ePassport) I believe now have an encrypted RFID with biometric info - which shields itself when it’s closed. You can tell if yours is one of the ePassports I think, by whether it has the little rectangular logo on the front. Older passports without the RFID technology don’t have that logo.
The passport card also has an RFID chip - which doesn’t have as much info, but it won’t shield itself- so it can in theory be read remotely.
I believe however it will only potentially broadcast an identifying number. Still probably good to keep it in the sleeve State provides with it.
I got an e-passport. And I keep the card in the little shell they sent with it, since they said to do that, and I am a good citizen who follows orders. Wish all my credit cards came with those. My only gripe is that the picture on the passport card is washed out, it looks over exposed, yet it is the same picture on my passport since I got them at the same time.