The passport card is issued with a protective sleeve that makes the card RFID unreadable while in the protective sleeve. I think the protective sleeve contains metal and it basically makes that impenetrable to snoops Due to the novelty I am carrying my passport card around with me in the protective sleeve
Ah, I didn't know that!
After receiving my passport, I actually considered applying for the pass card, since it would eliminate the need to submit my natz certificate again (as well as provide another proof of citizenship), in case I lost the passport (I'm very careful with important documents, but things happen). However, upon examining form DS-82, I learned that I'd have to submit my passport or natz certificate in order to obtain the pass card. I ended up deciding against it.