| 摘要 |
The delivery of special, preselected mail to a mailbox is detected and announced by including a piece of magnetic material or a metal object with the envelope. A magnetic detector or metal detector, within the mailbox, senses the presence of the magnetic material or metal object and actuates a radio transmitter, at the mailbox, which sends a signal to a radio receiver. Upon receiving the radio signal, the radio receiver activates a telephone answering device, or an automated building control or surveillance center having remote interrogation access or capable of sending an announcement so that a person at a distant telephone can be advised of the mail delivery. Electric wiring may be utilized in lieu of radio transmission.
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