M & S use contactless payment. They say if your purchase is up to £20, you don't need to enter your pin. I disagree with this as if you lose your card then someone could keep going in and spending £20, you've soon lost £100. It goes against the safety and security of using pin numbers to access payment.
If you have a debit card with a symbol on it that resembles the wi-fi signal symbol then you have the facility for contactless payment. The upper limit is around £20 and you just tap the card against the reader - you don`t have to use your PIN.
Faraday cage (named after Michael Farady) - an enclosure made of conducting material that conducts external electrical fields, keeping safe the contents from damage by those fields (recalled from memory - 'O' Level Physics - not cribbed). An aircraft acts as a Faraday cage when struck by lightning.