To report that an indoor sound is being transmitted outside a room to an inhabitant who is transmitting the sound by an audiovisual means.
An interphone indoor master telephone 2 installed indoors is provided with a voice switch 28 for switching transmission and reception states by comparing the signal level of a transmitted sound picked up by a call microphone 21 when calling a door phone slave telephone 1 installed outdoors while sound is being transmitted to the air, and the signal level of a received sound picked up by a microphone 12 of a door phone slave telephone, a transmission- reporting LED 25 that lights up when the transmitted sound is being transmitted to the door phone slave telephone from the interphone indoor master telephone to report to the transmitter that the indoor sound is being sent into the air outdoors, and a comparator 29 that receives a reference level from a voice switch and a comparison level as the comparison result between the signal level of the transmitter and that of the receiver to drive the transmission- reporting LED when the signal level of the transmitter becomes larger than that of the reception signal and hence the comparison level becomes larger than the reference level.
ISHII MASAHIRO
YAMAMOTO MASAO
Next Patent: AUTOMATIC METER-READING SYSTEM UTILIZING DIGITAL TELEPHONE LINE NETWORK