But I’m not crazy. The foil is only there to block the scanners. The bank sent out the new credit card a while ago, and it has a chip in it. After reading about the potential risks, it seemed like some shielding wouldn’t hurt anything. But how to know if the shielding worked?
At one work site, I get access to the facility by putting my id card against a scanner. This works even if I just hold my wallet up to the scanner. This seems like a reasonable basis for testing. The first thing I put in my wallet was a piece of what seemed to be metalized paper from a coffee package. Holding up my wallet still activated the door, so a coffee bag probably will not block the scanners the men in black would carry if there were men in black following me.
Next time I went out to that site, I folded up four layers of regular aluminum foil and put that in my wallet. The scanner didn’t work. A week or so later I tried it again, and this time scanner did read my card through the foil. Thinking it might be because the foil had compressed, I opened up the foil and interleaved a piece of paper. My knowledge of electricity and magnetism is close to the cargo-cult level, you see. Anyway, this seemed to work, but I’ll test it again from time to time.
If I come across some sheet copper I’ll try that too. A couple of business-card size pieces of copper with the Lord’s Prayer engraved on it would probably excite less interest than a packet of aluminum foil.