| 摘要 |
The device, intended to be mounted on the receiver of a telephone apparatus, can be engaged manually at the start of a telephone conversation and enables the user to hear a characteristic sound at regular intervals during a certain time period which may range from 10 to 30 min, for example. It includes a mechanical movement, the engaging of which is brought about through the winding up of a motive spring by means of a pusher. The sound is produced by percussions transmitted through the casing of the telephone receiver to the earpiece, using the casing as a phonic conductor.
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