Have you ever had trouble swiping your older, more-used credit cards through a card reader? Has the cashier sighed heavily and cast an annoyed glance in your direction as he or she finally gives up and types in the number manually? Next time, try the handy plastic bag solution.

There are tiny particles embedded in that magnetic strip on the back of your card. When the card is “swiped” through the reader, those particles are translated into binary code and transmits your card number (and other pertinent information) to the computer at the bank or wherever the merchant transmits the data for verification. As a card gets older and more worn, slight surface defects might occur in the magnetic strip that could corrupt the data stream. (The machine might read a zero where there isn’t one, and kick back your card as being invalid.)

Increasing the distance of the card surface from the reader even a few thousandths of an inch often improves the signal-to-noise ratio, causing the electric eye to skip over the “ticks” in the magnetic strip. The easiest way to accomplish this is to place a strip of clear cellophane tape over the strip, but since most consumers don’t carry a roll of Scotch tape with them, a plastic shopping bag will do the trick. Place the card in the bag, pull the bag tight around the card, and swipe it. In many cases, the card will now clear. Of course, we know that once you get home you’ll immediately apply for a replacement card, so that you won’t be holding up the line like that again.