QR codes were originally invented in Japan as a way to track machine parts but recently they have been adapted to contain all kinds of information that can be scanned by smartphones and specific action can be taken. In the case of GroupDeal, when your customers print out the coupons it will include a QR code which when the merchant scans it will connect to your website and instruct it that the coupon has been used. If the person tries to use the coupon again it will tell the merchant that the coupon is no longer valid.

This quick scanning method will help keep down the inevitable queues that will form from all the people using their coupons and is a much quicker way of trying to match up individual codes from the backup sheet of paper they can print out.