Near Field Communications is the process of bringing a compatible device up to a compatible terminal to perform an action. A common expample is using your phone, or tap to pay with a credit/debit card to pay for something. Another use for NFC is to use it to gain access to particular areas. Every NFC key will have their own ID number which defines whether that device has access or not. By replacing the key, there is little chance for a bad actor to gain access to a particular premise since the device stolen can be disabled, but a physical key requires an expensive locksmith.