Patent ID: 7555286

Claim:
An authentication card, which is installable in a portable apparatus that is carried by an owner, and that performs wireless authentication for another authentication card that is installed in another apparatus, the authentication card comprising: a storage portion for storing data of a call signal, an identification code of the authentication card, and an identification code of the other authentication card; a transmission portion that transmits the stored data of the call signal or the stored data of the call signal and the stored identification code of the authentication card by means of a wireless signal having a predetermined transmission level; a reception portion for receiving the identification code of the other authentication card that is transmitted by means of a wireless signal from the other authentication card in response to the transmission of the transmission portion; a judgment portion for judging whether a signal level of the transmitted identification code received by the reception portion is equal to or greater than a predetermined value and for judging whether the identification code received by the reception portion matches the identification code of the other authentication card stored in the storage portion; and a warning portion that outputs a warning signal to the portable apparatus upon, as a result of the judgment by the judgment portion, the level of the transmission of the identification code received by the reception portion being less than the predetermined value and upon the identification code received by the reception portion and the identification code of the other authentication card stored in the storage portion not matching.