| 摘要 |
A self-contained door alarm device is constructed with a housing, preferably fabricated from a high-strength insulator, such as ABS plastic, adapted to be secured above the upper edge of the door, to the doorframe. The alarm device contains a battery-operated tone generator operating in the audible frequency range, coupled to a small speaker. The power supply, preferably in the form of dry-cell batteries, is connected to the tone generator by a switch comprising a conductive strip mounted internally to the device housing, and provided with an elongated slot, and a conductive elastic spring anchored inside the housing and extending downwardly through the aforementioned slot to a position interfering with the plane of travel of the door upper edge. In the case of doors opening outwardly, the spring contact may be operated by a bracket attached to the door panel, along its upper edge. Movement of the spring contact due to entrainment by the door causes contact with the conductive strip and powers the tone generator, which in turn causes a tone to be emitted by the speaker.
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