| 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 authenticating a user, the personal authentication device comprising: 
            a memory storing instructions; and 
                at least one processor configured to execute the instructions to perform: 
                acquiring acoustic characteristic of the user from an acoustic signal transferred to a head of the user; 
                determining whether the 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 attachment trouble as to how the user wears the personal authentication device based on the acoustic characteristic of the user or the feature value extracted from the acoustic characteristic, 
                wherein the at least one processor is configured to execute the instructions to further perform: 
                when detecting that there is the attachment trouble as to how the user wears the personal authentication device, giving feedback to the user that it is not there is a lack of suitability as to person authentication of the user. 
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