Devices, systems, and methods are disclosed which relate to an NFC-enabled security token that is removably coupled to a mobile device. The security token may be provisioned with the information by the mobile device, then decoupled from the mobile device and used to authenticate the user or perform a transaction at a POS terminal equipped with an NFC reader. The security token includes logic for user-controlled restrictions on allowable purchases, such as payment limits, timeouts, vendor identifiers, allowed purchases, and location-based restrictions. The security token is further equipped with “self destruct” security features, such as deactivating itself or erasing any sensitive information upon being unable to contact the mobile device for a specified duration, or being subject to an unauthorized or restricted transaction, until such time as it is re-coupled to the mobile device.