| CPC G06F 21/32 (2013.01) [A61B 5/1171 (2016.02); G06F 21/34 (2013.01); G10L 17/02 (2013.01); G10L 19/02 (2013.01); G10L 25/06 (2013.01); G10L 25/51 (2013.01); H04R 1/10 (2013.01); H04R 1/1041 (2013.01); H04R 1/1091 (2013.01); H04R 1/26 (2013.01); H04R 1/46 (2013.01); H04R 3/00 (2013.01)] | 9 Claims |

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1. A personal authentication device worn by a user to be authenticated, the personal authentication device comprising:
a memory storing instructions; and
at least one processor configured to execute the instructions to perform:
determining whether an acoustic characteristic of the user or a feature value extracted from the acoustic characteristic satisfies a predetermined condition in accordance with an attachment trouble rule; and
detecting that there is an attachment trouble of the personal authentication device when the acoustic characteristic or the feature value satisfies a predetermined attachment trouble rule, wherein
the attachment trouble rule includes
(i) sound pressure at natural vibration wavelength corresponding to a distance between an earphone and an eardrum of the user is a constant multiple or half of a predetermined reference, or
(ii) maximum peak value of sound pressure within a frequency band corresponding to the distance between the earphone and the eardrum of the user is a constant multiple or half of a predetermined reference, and the maximum peak value of sound pressure is higher than two adjacent peaks within the frequency band corresponding to the distance from the earphone to the eardrum of the user.
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