Here's an abstract of the KLMK patent. Filed in 1993, patent awarded in 1995. How did they know back then we'd all have smartphones? :)
"An electronic paperless couponing system in which a store provides shoppers with an electronic communications device having a display screen for display of a graphic of a redemption coupon that represents a discount for an item in the store available for purchase. The communication device has a selection button to enter the selection of the coupon indicating the user's desire to redeem the coupon and a memory to record the selection until the shopper reaches the checkout counter and deducted from the purchases when it is determined that the item subject to the discount has been purchased."
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