it's actually a little envelope type thing that has a silver lining. I think I've read you can use foil too, but yes, apparently they can scan the cards in your purse. I also think they can scan gift cards on display for sale, then somehow know when they are bought and filled with $$. it's annoying that we are so unsafe now...........
This only applies to the newer contactless credit cards that use RF technology rather than a magnetic strip to transmit data and the chip is only readable out to about 4 centimeters so the thief would have to get pretty close (although cards carried in your back pocket might be a little more susceptible to this).
If you have a standard magnetic strip type card then your card can't be scanned remotely.