| 摘要 |
<p>The optical viewing device described comprises, in combination, an optical viewing tube for securing through the thickness of the door, an "outside" unit for attachment to the outside of the door and engaging around one end of the optical tube and an "inside" unit for securing to the inside of the door around the other end of the viewing tube, the "inside" and "outside" units including an audio microphone/ speaker device to enable a caller audially to identify himself and the outside unit including a self-contained lighting unit to illumlnate a caller. With such a device, a person inside the door can determine the identity and purpose of a caller before opening the door.</p> |
