It affects the UX somewhat, but since it has to be in proximity (implying data contact) to your phone to operate, you could just move the "switch active card" feature to the mobile app, not the Coin itself, then you wouldn't have to worry about people in posession of the Coin (e.g., when you put use it to pay the bill in a restaurant) toggling through the other cards stored on it for nefarious purposes. Or, for less impact on UX, put a "lock active card" option on the mobile app, and still leave the actual card switching on the Coin.