| 摘要 |
<p>The do-not-disturb unit only allows a subscriber's telephone to be called by specified persons. The unit consists of a device that responds to incoming call signals and suppresses the telephone bell. Specified persons can call the number by executing a coding procedure with their calls. The prearranged code is made up of an incoming call, a pause and then another incoming call, and so on. The times between calls are counted and registered as the incoming code. Only when the code is correct does the telephone ring.</p> |
