Coin uses a low-power Bluetooth signal to communicate with the app. If you ever leave your Coin behind while buying coffee, your phone will receive a notification asking whether you left without remembering to take your card. A phone is not required to use the card, however. Photo 4 of 5 in Slim Down Your Wallet with a Card That Does the Work of Eight Credit Cards by Dominik Sklarzyk

Slim Down Your Wallet with a Card That Does the Work of Eight Credit Cards

4 of 5

Coin uses a low-power Bluetooth signal to communicate with the app. If you ever leave your Coin behind while buying coffee, your phone will receive a notification asking whether you left without remembering to take your card. A phone is not required to use the card, however.