Can someone read information off my contactless credit or debit card without my knowledge?

While extremely unlikely, it is technically possible. Since the cards are designed to be read from up to 10 centimeters away, a criminal would have to get extremely close to you with a reader. But remember, the issuer of your card and the payment brands have put security measures in place to protect you, so even in the unlikely event that a criminal has read something off your contactless card, he or she can’t do anything with it.

More information: http://www.smartcardalliance.org/pages/publications-contactless-payment-…