Q. Can I lock my Coin?
A. Currently you cannot lock your Coin, but you don’t have to. Coin will automatically deactivate if it loses contact with your phone for a period of time that you configure in the Coin mobile app. In addition, Coin can disable functions like the button to select a card based on proximity to your phone.

So if the thief can locate the skimmer close enough, they can cycle through and skim all your cards (within a determined window of time).