Hearing dog: a dog trained to assist a deaf or hearing-impaired person by signaling the occurrence of certain sounds, such as a ringing telephone or doorbell.

被训练成通过发出类似于电话铃或门铃声等信号，给聋子或听力受损者提供帮助的导聋犬。

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He came downstairs on hearing the doorbell and was attacked as he opened the door of the family home in Roath.

BBC: Jason Richards and Ben Hope - artist impression