We gave this a lot of thought and came up with an ingenious answer....the curved shape!The curved shape of the Card Holder serves two purposes... Firstly it beautifully conforms to your body shape so you don't feel it in your pocket and secondly it places a slight curve in the cards to help hold them in place. Having said that, one card only is not too secure. Two cards are good, three and 4 cards are best. Alternately you can take maybe one, two or three cards and a few folded cash notes.During our research phase, we found that very few people would only take one card with them.They would, at the very least usually take one card and a bit of cash, and in this situation, the card and cash is secure. We have had more than 30 people road testing prototypes for the past 18 months and not a single person has reported any problems with card and/or cash security with the Card Holder.