| 摘要 |
A mobile communication device, such as a mobile phone, which comprises a processor which is configured to process requests for authorisation of use of a credential, such as a credit card, and the processor causes the device to emit a signal, such as an audible intermittent tone, the characteristics of which are indicative of the deemed importance of a particular use of the credential. Advantageously the owner of the device is alerted to the deemed importance of a use of a credential. For example, an intermittent tone of characteristic frequency is emitted by a mobile phone in relation to the monetary value of a transaction using a credit card.
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