| 摘要 |
PROBLEM TO BE SOLVED: To attain a case where no ring tone is produced to a mischievous switch-on operation by providing the 1st and 2nd hook switches of an indoor master unit, connecting these two switches in series, locating both switches so as not to be easily pushed at a time by a single hand and making these switches serve as a ring tone sounding speaker and a handset receiver respectively. SOLUTION: When a resident takes up a handset 8 after calling, the 1st and 2nd switches 7a and 7b of a hook switch 7 are turned off. Then a talking circuit 3 inhibits the talking with a ring tone generation circuit 5 nor the talking with a door slave unit 1 either. When the talking is permitted with the unit 1, a talking state is secured. When the handset 8 is set in its original state after the talking is over, the switch 7 is turned on and the circuit 3 stops its operation to end the talking with the unit 1. Thus, no ring tone is produced as long as both switches 7a and 7b are turned on at a time even though the handset 8 is taken up and the switch 7 is mischievously turned on.
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