| 摘要 |
PROBLEM TO BE SOLVED: To provide an intercom system for changing a call tone in an easily confirmable way when no reply comes in response to a call from an entrance slave unit. SOLUTION: When no reply comes from a master unit in response to a call from the entrance slave unit even for a lapse of a prescribed period of time, a ringer mode of a ringer tone volume produced from the master unit is made to be different from the mode of a first call with respect to a second call from the entrance slave unit. For example, the sound is made loud, the melody is changed or the number of ringing times is changed. Thus, even when the ringer tone cannot be confirmed because of absence of people around the master unit, the ringer tone can be heard. COPYRIGHT: (C)2004,JPO
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